python en
Counting list elements in Python: dict, Counter and hashing
I turn a list into a frequency table and check what the numbers represent, including missing categories, ties and the surprising equality of True and 1.
KajoData blog
Data, work and everything around them.
I write about data analysis, useful tools and changing careers. Expect examples you can check and ideas you can put to work.
Articles: 125
python en
Python lists: indexing, slicing and shallow-copy traps
I trace list operations through concrete positions and results, including the difference between a new outer list and independent nested data.
python en
Reading files in Python: text, CSV and import checks
I build a complete file-reading example and check paths, Unicode, empty fields and zeros before calculating a result.
SQL
SQL CTEs: WITH and a monthly report step by step
I name calculation stages and build a report that retains empty months. Learn CTE scope, aggregation, missing values and how to check each result.
SQL
SQL formatting: readable code and verified results
I separate SQL style preferences from calculation changes. Use a small dataset to check aliases, joins, filters and safe refactoring.
SQL
SQL SELECT: columns, filters and predictable results
Start with SELECT * and build a result you can verify. I explain column selection, filters, missing values and resolving ties before applying LIMIT.
Career & business
How to plan a data analysis project: question, scope and acceptance
I show how to turn an analysis idea into a project you can finish: define the question, inspect the data, limit the scope and deliver an answer someone can use.
Career & business
IT conferences for introverts: preparation, conversations and a calmer plan
I organise conference attendance around a useful question, a few meaningful conversations and one idea to test afterwards. You do not need to meet the entire room.
Career & business
How to receive feedback: from a difficult comment to a specific change
I separate difficult feedback into facts, interpretations and a next step. Here is how to ask for specifics, disagree constructively and evaluate an improvement.
Career & business
Data analysts and AI in 2026: fundamentals for checking results
I show what to delegate to AI, which decisions need explicit ownership and how to detect working code that produces a wrong answer. We walk through a small SQL example and a way to deliver verified analysis.
Career & business
Data analyst collaboration: 6 behaviours that make work harder
I look at observable behaviour rather than labels: what blocks a team, how to discuss it and how to check improvement. With examples of feedback, knowledge transfer and reviewing your own habits.
Career & business
5 junior data analyst mistakes and work habits that help
I walk through five habits to improve in your first analyst role, from agreeing on a report's purpose to discussing your development. With examples of a brief, a blocker update and a handover, without promises of job security.
Career & business
Data analyst career paths: management, data science or business?
I use one delivery problem to compare the work of a manager, a data scientist and a business specialist. Then I show how to plan a small trial of your chosen direction.
Career & business
Grow in your team: make your work visible and help others
I explain how to choose useful work, communicate progress and help colleagues without taking over their entire queue. You will also get an example of a contribution record and a way to discuss your next responsibilities.
Career & business
Your first data analyst job: technical skills and collaboration
I walk through one small analysis, from a vague request to a checked answer. Learn how to agree on definitions, ask for useful feedback and show your contribution in a portfolio.
Career & business
What a Data Analyst Needs to Know: 10 Skills You Can Test on a Project
A list of tools tells me little about what you can deliver. I use one small project to show how to test ten analyst skills, from clarifying a question to explaining a recommendation.
Career & business
Data analyst career map: roles, responsibilities and your next step
I explain six areas of data work and the evidence that can show readiness for each. Build your own career map around real responsibilities and a small practical project.
Career & business
Data analyst technical interviews: an answer, an example, a limitation
Knowing a definition is a starting point. I show how to explain a technical answer, predict a small example's result and identify the limitation that matters.
Career & business
Financial KPIs: COGS, contribution margin, OPEX and cash
Positive profit can coexist with falling cash. Follow one cost, margin and payment model with reproducible calculations and explicit assumptions.
Career & business
Logistics KPIs: time, timeliness, returns and cost
One order queue shows how to measure time, fulfilment and cost without hiding delays. Separate orders, parcels, product units and available inventory.
Career & business
Ecommerce KPIs: CAC, AOV, retention, LTV and payback
One shop, six orders and consistent definitions. Learn to calculate ecommerce KPIs and distinguish sales, contribution after costs and predicted customer value.
Career & business
How to learn data analysis effectively: five principles
Move from completed lessons to skills you can demonstrate. Practise, revisit and assess progress through concrete tasks, without promises of a quick promotion.
Career & business
Data analysis methods: from business question to decision
Conversion falls while group rates stay unchanged. A shop example shows how to choose an analytical method and establish what remains unknown.
Career & business
Data problems in companies: definitions, collaboration and ownership
Three reports show different order counts. I use one example to explain how to investigate the difference, agree on a definition and decide who will fix it.
Career & business
Power BI skills for analysts: five areas to practise
Build a report you can explain and check. Explore five Power BI skill areas with a tiny exercise covering filters, shares and missing amounts.
Career & business
How to analyse your own data: a first small project
I work through a small reading diary, from defining a row to calculating averages, evaluating a target and explaining missing observations.
Career & business
Tableau or Power BI? How to choose as a beginner
Start with your goal and audience. Understand free editions, local work and publication, then compare the tools through one consistent exercise.
Career & business
5 statistical mistakes analysts make: check the conclusion
I show how correct figures can support an incorrect story, and how to check denominators, samples, distributions and the scope of a recommendation.
Career & business
Analytics Engineer: data models, tests and maintenance
A shared table needs ownership, definitions and checks. Explore analytics engineering through an order model and the changes its team must maintain.
Career & business
SQL for data analysts: from question to verified result
A query can run successfully and still answer the wrong question. Work through order grain, joins, missing amounts and a reproducible reconciliation.
Career & business
Meetings and time for analysis: plan a workable week
A calendar needs room to carry out decisions. Explore a weekly plan covering analysis, meetings, communication, breaks and unexpected work.
Career & business
Outlook, Slack and Teams notifications: choose useful signals
Calmer work starts with useful signals and clear team expectations. Explore application settings and a practical way to verify urgent exceptions.
Career & business
Animation engineering: a conversation with Adrianna Bielak
How does code make movement respond to a player? I revisit my conversation with Adrianna Bielak and explain the technical ideas through simple examples.
Career & business
15 KPIs I want every data analyst to understand
Acquisition gets cheaper, sales go up, and somehow the money does not follow. Here is how I connect 15 business metrics and check the story behind the cheerful green arrows.
Career & business
Data Analyst vs Business Analyst vs BI Developer: roles in a project
I use one project to distinguish clarifying a need, investigating data and building a reporting solution that remains useful after delivery.
Career & business
How Power Query works: from a raw file to a repeatable process
Power Query remembers how to prepare data. I explain what it repeats, how to verify the result and why a new source file can still require a change to the rules.
Career & business
Can a humanities graduate become a data analyst? My route from literature
I studied Polish literature. Before analysing data professionally, I was trying to understand where my money went. Here is that journey, the skills I could bring with me and the technical work I still had to learn.
AI
GPT-5 vs Gemini 2.5: what my analysis test showed
I revisit four tasks used to compare GPT-5 and Gemini 2.5, explain what the results support and show how I would check a model's analytical work.
Career & business
5 reasons Excel still belongs in an analyst's toolkit
I use one small example to show where Excel helps, what to check after a refresh and how to deliver a workbook someone else can understand.
Career & business
Why I enjoy being a data analyst: four reasons and one example
I enjoy the moment when numbers begin to explain a specific problem. I work through a question about late deliveries to show what makes analytical work satisfying to me.
Career & business
Beginner data analyst mistakes: how to recognise and correct them
Knowing a tool can feel like independent analysis. I show how to check your foundations, limit a project and explain a result whose limitations you understand.
Career & business
Data analyst or programmer? Try the work before choosing the title
Before choosing a career from a list of technologies, try solving a small problem in two different ways. I compare the work, the responsibility and what you can learn from each experiment.
Career & business
Data Analyst vs Data Scientist: tasks, responsibility and choosing a path
I use one delivery scenario to show how the question, output and checks change between analysis and predictive modelling.
Career & business
Data analyst disadvantages: how to evaluate a role and its daily work
I explore the less comfortable parts of analysis and the questions that help you understand how a particular team actually works.
SQL
A histogram in SQL: from orders to a customer distribution
The average customer places a few orders. But how many buy once, and how many return regularly? I build the distribution step by step, including the mistakes that make valid SQL answer the wrong question.
SQL
SQL pivot tables: CASE WHEN, COUNT and the traps around NULL
A pivot can look correct while losing orders. I show how to count categories, distinguish zero from missing data and reconcile the columns with the source.
Career & business
Data cleaning: five steps that preserve the meaning of your analysis
Removing duplicates takes a click. Deciding what counts as a duplicate takes thought. I explain five stages of data cleaning and how to check that the tidy result still answers the original question.
Career & business
LinkedIn for an analyst job search: profile, projects and routine
I show how to connect a clear profile, useful conversations and vacancy reviews into a process you can assess beyond view counts.
Career & business
Data analyst CV mistakes: show your skills and experience clearly
I show how to replace general claims with accurate descriptions of work that a reader can understand and discuss in an interview.
Python
Python variables, data types and operators: a practical starting point
Two names can share one list, and the text False can behave like true. I explain Python basics through a small data task, including the quiet mistakes that change your results.
Excel
VLOOKUP, HLOOKUP and XLOOKUP: one practical Excel example
A formula can return a number and still point to the wrong product. I walk through a small product lookup, then deliberately break the data to show what needs checking.
SQL
Advanced SQL queries: CTEs, windows and rankings in one example
A query with three CTEs can look impressive while calculating the wrong sales total. I build one analysis step by step, keeping track of row meaning, missing values and the order of calculations.
python en
Python basics: from a variable to a checked pandas report
I follow one complete example from reading orders to checking inputs and explaining a grouped report without hiding missing amounts.
SQL
SQL basics: from your first table to a result you can explain
A query can run successfully and answer the wrong question. I work through six orders to show how selection, grouping, missing values and result checks fit together.
Excel
Advanced Excel formulas: calculations, lookups and error checks
A useful formula produces a result you can explain and verify. I use six records to connect calculations, lookups and text processing in a readable worksheet.
Career & business
Difficult interview questions: prepare answers you can explain
I show how to turn real experiences into clear answers that hold up when the interviewer asks what you did and how you checked the result.
Career & business
Data analysis for introverts: focused work and clear communication
You can prefer quiet work and still collaborate well. I look at the conversations involved in data analysis and how to give them a useful structure instead of constantly improvising.
Career & business
Why can’t I find a job? How I approach a career change into analytics
Another course finished, another CV sent, still no reply. I break a career change into decisions you can act on: the role you target, the experience you build and the evidence you show.
AI
AI in everyday life: what I use it for and what I check
AI can save me a lot of clicking. It can also produce a very fluent explanation of something completely wrong. Here is how I choose tasks, give useful instructions and check the result before celebrating the time I saved.
Career & business
Designing a data dashboard that helps someone make a decision
An attractive dashboard can still suggest the wrong conclusion. I use delivery data to connect the reader's question, correct measures and a clear layout with a practical usability test.
Career & business
How to become a data analyst: learning, a project and your first applications
I explain how to connect tools through one project, document your skills and prepare to discuss the work of a data analyst.
Career & business
Who can work as a data analyst? Four traits you can practise
I show how to explore your fit for data analysis through observable behaviour, a worked example and useful feedback.
Excel
Array formulas in Excel: from one cell to a complete list
One formula can calculate six values, select matching rows or create a list of categories. I explain how to predict its output and catch mistakes before they reach a report.
statistics
Z-scores and standard deviations: calculation and interpretation
I explain distance from the mean, show how to check the calculation and identify what a z-score cannot establish about rarity.
SQL
SQL JOIN types: how I combine tables and check the result
Two tables, one JOIN and suddenly revenue doubles. Unfortunately, only in the report. Here is how I choose a join for the question and check that the result still represents the right things.
Career & business
Why I Really Became a Data Analyst: On Cigarettes, Shakespeare, and the Art of System Building
Discover the true story of how a Polish literature graduate went from tracking cigarettes in Excel to becoming a Data Architect earning 25k PLN.
Career & business
Will AI Replace Data Analysts and Consultants? On Artifact Reduction, "AI Slop", and the True Human Value in Data
Will AI make data analysts and consultants obsolete? Discover why generating slides or code isn't enough and where true human analytical value lies.
Career & business
Do I Regret Leaving My Full-Time Job? On Courage, Fear, and Forging Your Own Path
Wondering if you should quit your job? Read my story of transitioning from a Data Architect to a business owner. Fear, courage, and tough IT career choices.
Career & business
I Lie, Therefore I Work? What an Ex-Google Recruiter Says About Job Interviews (And Why She's Right)
Is honesty always the best policy in a job interview? I analyze advice from a former Google recruiter to help you strategically land a job in tech and data.
Career & business
7 Levels of Job Hunting in Data Analytics and Tech: Where Are You and How to Stop Wasting Time?
Applying for jobs with zero response? Discover the 7 levels of job hunting in data analytics and IT. Identify your mistakes and speed up your hiring process.
Career & business
6 Unconventional Career Tips for Data Analysts: The Brutal Truth About Corporate Promotions
Discover 6 politically incorrect tips to fast-track your career in data analytics. Learn how to strategically use Excel, SQL, and psychology to win in the corporate world.
Career & business
From Imposter Syndrome to Artificial Intelligence: The Real Face of a Data Analyst's Career
Discover the unvarnished truth about working as a data analyst. Kajo Rudziński breaks down the myths surrounding English requirements, imposter syndrome, and AI.
Career & business
A New Era in Technology and Data
Wondering what an AI Engineer is and if it's worth the pivot? Discover the career path, salary expectations, and necessary tools for this innovative IT role.
Career & business
What is AI Really Stealing From Us? The Hidden Cost of Automation
Is artificial intelligence destroying our critical thinking and writing skills? Discover how to maintain your human competitive edge in the tech market.
Career & business
Behind the Scenes of IT: What the Tech Hype Won't Tell You. A Conversation with Natalia Kierczuk
Discover the brutal reality of working as a business analyst in IT. Natalia Kierczuk (IT bez kodu) reveals industry myths, AI's impact, and corporate secrets.
Career & business
English in IT: How to Stop Being Afraid and Start Promoting Yourself? A Conversation with Wiktoria Sitko
Discover why a B2 level isn't enough in IT and how to effectively learn English to accelerate your career. Interview with Wiktoria Sitko on language blocks and learning.
Career & business
Fear of Being Fired? Don't Just Wait—Take Control of Your Career
Afraid of losing your job? Learn how to build a financial runway, develop new skills, and create a strategy to turn a crisis into a career success.
Career & business
Every Stage of Career Change: A Psychological Roadmap for Switching Professions
Discover the real stages of a career change. Learn the psychological roadmap of switching professions – from the first spark of interest to success in a new industry.
Career & business
What’s the Point of It All? On Ambition, Choosing the Right Walls, and Doors You Can’t See Yet
Struggling with career stagnation? Explore why a career change to data analytics is about more than just tools—it's about opening doors to a future you can't see yet.
Career & business
We need to talk honestly: The job market and your career
Is the IT job market in crisis? Let's analyze the facts, myths about AI, and the differences between overthinking and effective action in the data analyst profession.
Career & business
When Should You Actually Lie in a Job Interview? The Brutal Truth About Recruitment
Is honesty always the best policy? Discover 5 specific situations where lying or stretching the truth in a job interview is necessary to land your dream career.
Career & business
AI Was Supposed to Replace Us. Yet the Data Tells a Different Story
Is AI really replacing jobs in tech? Data from the No Fluff Jobs report shows a surprising trend: more IT job offers, fewer applicants, and growing demand for data specialists.
Career & business
9 Interview Questions That Actually Decide Whether You Get the Job
9 common interview questions explained from a recruiter’s perspective. Learn what employers are really testing and how to answer without ruining a good interview.
Career & business
Ambition Is Not Arrogance. Why Preparation and Proactivity Actually Matter
Why ambition is often confused with arrogance and how preparation and proactivity shape long-term career growth without motivational nonsense.
Career & business
The Backend of Analytics, Career Switching, and the Meaning of Working with Data
What is backend data analytics and why dashboards alone are not enough? A deep interview on BI, data engineering, AI, and career switching.
Career & business
Data Cleaning Is the Foundation of Data Analysis. Why Data Analysis Is Actually Hard
Data cleaning is the foundation of data analysis. Learn why cleaning data takes so much time and how poor data quality breaks analysis and reporting.
Career & business
Four Fundamental Elements of a Successful Career Change
Thinking about a career change to data analytics? Learn the four fundamental elements that determine whether a career transition succeeds or quietly falls apart.
Career & business
Data as the New Oil? A Real Conversation About Big Data, Scaling, AI and the Future of Tech Jobs
What is Big Data in practice? A deep conversation about data scaling, data engineering, distributed systems and how AI impacts tech careers.
Career & business
How to Find a Job in 2026. Why Old Strategies No Longer Work
The job market has changed more than you think. Learn how to find a job in 2026, why old strategies no longer work, and what actually increases your chances.
Career & business
From Hospitality to Big Data. A Real Story About Career Change, Flow in Data, and Living Without a Strict Work-Life Split
What does a real career change to data analytics look like? An honest story about learning Python, working with big data, doubts, flow, and growth.
Career & business
Don’t Plan Your Career Too Rigidly. A Conversation About Work, Ambition, and Freedom
Is work-life balance really a myth? A reflective conversation about work, ambition, career choices, and life in data analytics.
Career & business
Why You Can’t Get a Job: On Career Change, Competition, and the Illusion of Balance
Struggling to land a job despite your efforts? Discover why “trying” isn’t enough. I share honest insights on career change, real competition in the job market, and why the illusion of balance might be holding you back.
Career & business
Freelancer or Full-Time Employee – The Truth About a Data Analyst’s Work
Wondering whether to work as a freelance or full-time data analyst? Discover the real pros, cons, and hidden pitfalls before you make your decision.
Career & business
When Is It Too Late to Change Careers? At What Age Does a Career Switch Still Make Sense?
Is it really too late to change careers after 40? Discover when a career switch still makes sense, how to use your experience as an advantage, and why fear can be your best motivation.
Career & business
A Good Job and the Confidence You’re Missing
How do you build confidence and grow your career in data analytics? Discover my journey from customer service to data architect — about hard work, learning, and finding real confidence at work.
Career & business
How to Really Use AI in Your Job Search — From Your CV to the Interview
Learn how to use artificial intelligence to make your job search faster and more effective. From writing a powerful CV and optimizing your LinkedIn profile to practicing for interviews and building a personal job-hunting system with AI.
Career & business
Motivation Is a Lie. That’s Why You’re Not Changing Your Job.
Most people believe motivation is the key to career change — but that’s a lie. In this article, I explain why motivation fails, what truly drives a successful career transition, and how to finally change your job with a clear plan and purpose.
Career & business
A Week in the Life of a Data Analyst – What My Job Really Looks Like
Ever wondered what a typical week looks like for a data analyst? From dashboards in Power BI and Tableau to SQL, Python, and team meetings – discover what daily life as a data analyst really involves and why this career is so dynamic and rewarding.
Career & business
How to Analyze Election Polls – Understanding Statistical Error and Why Polls Can Be Wrong
Learn how election polls really work. What does the margin of error mean, why can 1,000 people represent a whole country, and why polls sometimes get it wrong.
expert
What Does a Data Engineer Do? A Candid Conversation with Nieinformatyk
Zastanawiasz się, jak wygląda codzienność inżyniera danych? W tym wywiadzie z Darkiem Butkiewiczem (NIEINFORMATYK) poznasz kulisy tej pracy, realne technologie i wskazówki dla osób myślących o przebranżowieniu.
expert
Power BI is not Excel. A conversation on implementation, Copilot and training with Iga Kwiecińska
Discover what implementing Power BI really looks like and why Copilot won’t replace analysts. Iga Kwiecińska shares practical insights on common mistakes, AI expectations and the role of live training in data analytics.
Career & business
How to Become a Data Analyst with No Experience? Izabela Witczak’s Real Story
Want to become a data analyst but have no experience? Discover how Izabela Witczak made it happen in just 9 months. Real advice, clear steps, and inspiration for your career switch into data.
Career & business
What to Do with a Weak Resume? 5 Strategies That Actually Work
Struggling with a weak resume? Learn how to improve your chances of getting hired even without experience. Real strategies to upgrade your resume and job search approach.
Career & business
The Modern Programmer – Interview with Kamil Brzeziński
What does a programmer’s job really look like today? In this in-depth interview, Kamil Brzeziński talks about AI, vibe coding, career advice, and the evolving role of developers in the modern tech world.
Career & business
The Job of the Future Doesn’t Exist. Here’s Why You Should Stop Chasing It
Does the job of the future really exist? In this article, I explain why chasing trendy job titles is a trap—and what skills you should focus on instead, especially in tech and data.
Career & business
AI won’t take your job. It will take your loneliness.
AI may not replace your job, but it can replace your loneliness. And that might be a good thing. Here’s how artificial intelligence is becoming a new kind of emotional support system.
Career & business
How to Get Your First Job as a Data Analyst During a Market Slowdown – 5 Smart Strategies
Looking for your first job in data analytics during a slowdown? These 5 strategies will help you land a role by searching smarter, not just harder.
Career & business
AI and the Future of Data Analysis: Will AI Replace Data Analysts?
Explore the transformative potential of AI in the realm of data analysis. Discover whether AI will replace data analysts or if it will simply reshape the role.
Career & business
Career Change After 30 - How to Make a Career Transition After 30?
Thinking about a career change after 30? Wondering how to make a career transition after 30 and start a new life? This article is for you!
bez kategorii
How to Successfully Transition into a Data Analyst Career: Essential Skills and Tips
Thinking about becoming a data analyst? Learn how to successfully transition into a data analyst career with these essential skills and tips.
expert
Data scientist vs data analyst - interview with Magda Kostrzewska
Main topic: data scientist vs data analyst. Magda is an experienced data analyst and data scientist, and in this interview...
expert
Interview with Jan Tymiński: The Role of DevOps in Today's IT World
DevOps is someone responsible for the infrastructure on which applications created by programmers and analytical systems provided...
Career & business
GPT 4o and Gemini Advanced or how new AI models will change the world
If you ever googled 'GPT 4o and Gemini Advanced' or you would like to know how new AI models will change the world, this article is for you.
Career & business
Job market crisis or is it difficult to get a job now
If you ever googled 'Job market crisis' or you would like to know is it difficult to get a job now, this article is for you.
Career & business
IT job market in Poland or is it still worth it to work in the tech industry
If you ever googled 'IT job market in Poland' or you would like to know is it still worth it to work in the tech industry, this article is for you.
Career & business
Why you don't need to look for a new job? My take on the value of staying with a company
If you ever googled 'Why you don't need look for a new job' or you would like to know a new job or why is it worth to stay in a company for longer, this article is for you.
Career & business
Motivation at work or how to change your mindset?
If you ever googled 'Motivation at work' or you would like to know how to change your mindset, this article is for you.
AI
ChatGPT in IT: Can Artificial Intelligence Hinder Your Career?
Is using ChatGPT in IT always a good thing? Can learning programming with AI hinder your career? As an enthusiast and educator...
Career & business
Professional Burnout and Impostor Syndrome – Experience of looking for a job in IT
Domething that affects many of us, whether we're job hunting or entrenched in our careers - professional burnout & impostor syndrome...
Career & business
How to Rediscover Lost Motivation? Insights from a Data Analyst
Have you ever felt like you just can't be bothered? Well, you're not alone. Actually, motivation loss is quite normal. Lost motivation...
Career & business
Active Listening, Giving Up, Mistakes That Can Cost You a Job in IT
I want to share my insights on five non-trivial mistakes (like lack of active listening or giving up) I see when conducting these interviews.
Career & business
Becoming a Data Analyst: the best way into in IT
The truth is that today becoming a Data Analyst is the best way into in IT.Shocking, right? Well, I want to convince you...
Career & business
Average BI Developer salary. Money in IT - interesting comparison
Average BI Developer salary. Money in IT - interesting comparison. Today, we're diving into the fascinating world of...
Excel
Python in Excel - a revolution from Microsoft and Anaconda
Python in Excel? Really? 😱Is this the beginning of the end for the Excel we know? Last week, Microsoft made a groundbreaking announcement.
AI
What is the ELIZA effect, or is chat GPT conscious?
Do you ever have moments when you wonder if Chat GPT is conscious? Well, let's talk about Eliza Effect. But before we get to the heart of...
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