Data Cleaning for Beginners: A Step-by-Step Checklist
Messy data is the normal case. This checklist keeps you from missing the usual problems.
Step 1: Look first. Run the Data Profiler to see the row count, blank cells and duplicate rows for each column. Keep a copy of the original file.
Step 2: Fix the shape. Remove duplicate rows, trim extra spaces and rename columns to simple names with no spaces. Data Transformation has steps for each of these, and you can see the effect of every step on the row count.
Step 3: Fix the values. Put dates in one format, change text such as 1,250 into a number, and make text case consistent so that Delhi and delhi are one value. Decide what to do with blanks: remove the rows, fill them with a value, or leave them and say so.
Step 4: Check and record. Profile the cleaned file again, compare the row counts before and after, and write down each step you took. A short list of cleaning steps is part of a good assignment, and Data Lineage can record them for you.
Everything runs in your browser and nothing is uploaded.
Related tool pages
- Delete Columns from a CSV File: Remove one or more columns from a CSV or Excel file and download the result. Free, in your browser, and your file is never uploaded.
- Reorder Columns in a CSV File: Drag columns into a new order, or send a column to the start or the end, in a CSV or Excel file. Free, in your browser, nothing is uploaded.
- Remove Empty Rows and Columns from CSV: Remove rows with empty cells, rows that are completely empty, or columns with no values from a CSV or Excel file. Free, in your browser.
- Find and Replace in a CSV File: Find and replace text in a column of a CSV or Excel file, then download the result. Free, in your browser, and nothing is uploaded.
- Change Date Format in a CSV File: Change the date format of a column in a CSV or Excel file, for example 09/03/2026 to 2026-03-09, or get only the year or month. Free, in your browser.
- Convert Excel Date Numbers to Dates: Turn Excel date numbers such as 46090 and unix timestamps into readable dates in a CSV or Excel file. Free, and your file stays in your browser.
How to use the Data Transformation: step by step
- Profile the file and keep the original.
- Remove duplicates, trim spaces and rename columns.
- Fix dates, numbers and text case, and decide about blanks.
- Profile again and write down the steps.
When to use the Data Transformation
- Clean a dataset for a class assignment
- Prepare data before analysis
- Remove duplicates and blanks
- Document your cleaning steps
Example
Input: plans.csv + customers.csv, key = id
Output: id, first_name, plan, amount
Frequently asked questions
Which transformations are available?
Join with a second file (inner, left, right, full), trim spaces, concatenate columns, change case, find and replace, split a column, rename, remove columns, reorder columns, remove empty rows or columns, filter rows, remove duplicates, sort and fill empty cells.
Can I run several steps?
Yes. Steps run from top to bottom and each one sees the result of the one before. You can reorder or remove them.
Can I join two files or combine columns?
Yes. Data Transformation lets you join two CSV or Excel files on a key (inner, left, right or full), and trim spaces, concatenate columns, change case, find and replace, split, rename, filter, sort, remove duplicates and fill empty cells. You choose the steps, check the result and download it. Your files stay in your browser.
Can I change the date format of a column?
Yes. Add a Change date format step, pick the column and the new format, such as 2026-03-09, 09/03/2026 or March 9, 2026. It reads many layouts, Excel date numbers and unix timestamps, and can also give only the year, month, weekday or quarter. If 03/04/2026 is unclear, you choose day first or month first.
Tip: Never overwrite the original file. Save the cleaned data under a new name.