Data Transformation: Join, Trim and Concatenate Files Online

Clean and reshape a file in a few clicks: join it with another file, trim, concatenate, filter and more.

Raw data is rarely ready to use. Names have extra spaces, first and last names sit in two columns, rows are duplicated, and the information you need is split across two files. Fixing this by hand in a spreadsheet is slow and easy to get wrong.

Data Transformation lets you load a file, add the changes you want, and see the result before you download. You can join with a second file on a key, trim spaces, concatenate columns, change text case, find and replace, split a column, rename or remove columns, filter rows, remove duplicates, sort, and fill empty cells.

Steps run from top to bottom, and each step sees the result of the one before it. You can reorder or remove a step at any time and the preview updates. A join can be inner (only matching rows), left (all rows of the first file), right (all rows of the second file) or full (all rows of both). Keys are matched ignoring case and extra spaces, so Ada@Example.com matches ada@example.com. A good order is to trim first, then join, then concatenate.

Your files are processed in your browser and are not uploaded. Every step is also written to Data Lineage, so you can show later exactly how the file was prepared.

Open the Data Transformation

Related tool pages

  • 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.
  • Join Two CSV Files on a Key: Join two CSV or Excel files on a key column with an inner, left, right or full join. Free, and your files stay in your browser.
  • Merge CSV Files by a Common Column: Merge two CSV files into one by matching a common column such as id or email. Choose inner, left, right or full. Free, in your browser.
  • VLOOKUP Alternative for CSV and Excel Files: Look up values from one file in another without VLOOKUP. Join two CSV or Excel files on a key and add the columns you need. Free, in your browser.
  • Join Two Excel Files on a Key Column: Join two Excel files on a key column and download the combined result as Excel or CSV. No formulas, free, and your files stay in your browser.

How to use the Data Transformation: step by step

  1. Open Data Transformation and load your first file.
  2. Load a second file if you want to join.
  3. Add steps, such as Trim spaces, Join and Concatenate.
  4. Check the result and download it.

When to use the Data Transformation

  • Add plan details from one file to a customer list
  • Combine first and last name into one column
  • Clean spaces and casing before a database import
  • Remove duplicates and sort a contact list

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, 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: Add Trim spaces before a join. A stray space in a key stops two rows from matching.