concat to Stack and Append
Combining tables vertically or sideways.
concat to Stack and Append is a free Data Science Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Data Science Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Stacking, Not Matching
Sometimes you do not match on a key, you just pile tables together. That job belongs to concat, not merge.
Stack Rows Vertically
Pass a list of frames to concat and it stacks them on top of each other into one taller table.
pd.concat([jan, feb, mar])A Classic Use Case
Concat shines when you have monthly files with the same columns and want one combined dataset for the year.
Reset the Index
Stacking keeps each frame's original index, so labels repeat. Use ignore_index to renumber rows cleanly.
pd.concat([jan, feb], ignore_index=True)Glue Side by Side
Set axis=1 and concat joins frames horizontally, placing their columns next to each other by row position.
pd.concat([features, labels], axis=1)Columns Align by Name
When stacking rows, concat lines up columns by name. Order does not matter, only the labels do.
Missing Columns Get NaN
If one frame is missing a column the other has, concat keeps it and fills the gaps with NaN.
Keep Only Shared Columns
Want columns that exist in every frame only? Pass join="inner" to drop the rest during concat.
pd.concat([a, b], join="inner")Tag Where Rows Came From
The keys argument labels each chunk, building a tidy MultiIndex so you can tell the sources apart later.
pd.concat([q1, q2], keys=["Q1", "Q2"])append Is Gone
Older code used DataFrame.append, but it was removed. Reach for concat for every stacking job today.
concat or merge?
Quick rule: concat when you stack frames with the same shape, merge when you match rows on a key column. 🧩
Quick Check
You have twelve monthly CSVs with identical columns. How do you build one table?
Recap: Stacking With concat
You can stack frames by rows or columns, reset the index, control missing columns, and tag sources with keys. Great work!
Frequently asked questions
Is the “concat to Stack and Append” lesson free?
Yes — the full text of “concat to Stack and Append” is free to read here on the web, and the Data Science Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Data Science Academy course, upgrade to CoddyKit PRO.
What will I learn in “concat to Stack and Append”?
Combining tables vertically or sideways. You practise Data Science Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Data Science Academy?
No prior experience is required. Data Science Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “concat to Stack and Append” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Data Science Academy lesson?
Yes. Every Data Science Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Inner, Left, Right, and Outer
- Merge on Keys and Indexes
- concat to Stack and Append
- Diagnose Bad Joins