How to Merge Two Lists Online

Q: How do I combine two lists into one?

Open the Merge Lists tool , paste both lists, and choose Stack. That appends everything from List 2 below List 1. If you want duplicates removed automatically, use the Compare Two Lists tool and take the Union output instead.

"Merge" is one of those words that means something different depending on who you ask. Appending one list below another is a merge. So is alternating items. So is joining pairs of items into one line. The right mode depends on what you're actually trying to produce.

Try the merge modes on your own lists.

Open Merge Lists Tool →

Stack: append one list below another

Stack is the simplest mode. Everything from List 1 comes first, then everything from List 2 below it. The output has as many lines as both lists combined. Order within each list is preserved.

Use Stack when you want to:

Combine two exports from the same source into one file
Add new items to the end of an existing list
Concatenate two batches before deduplicating

Stack does not remove duplicates. If the same item appears in both lists it will appear twice in the output. To merge and deduplicate at the same time, use the Compare Two Lists tool and take the Union output.

Interleave: alternate items from each list

Interleave takes one item from List 1, then one from List 2, then back to List 1, and so on. With two lists of 4 items each you get 8 output lines in the order A1, B1, A2, B2, A3, B3, A4, B4.

Use Interleave when you want to:

Pair a list of questions with a list of answers
Create alternating sequences for A/B testing
Shuffle two parallel datasets together by position

You can increase the group size to take more than one item from each list before switching. A group size of 2 gives you A1, A2, B1, B2, A3, A4, B3, B4.

Row Join: combine same-position items into one line

Row Join pairs the item at position 1 from List 1 with the item at position 1 from List 2 and joins them into a single output line using a separator you choose. Position 2 with position 2, and so on.

If your separator is a comma, two lists of 4 items each produce 4 comma-separated output lines. Think of it as building a two-column CSV from two separate columns.

Use Row Join when you want to:

Build CSV rows from two separate data columns
Attach a label to each item from a parallel list
Combine first name and last name columns into full names
Reconstruct data that was split across two files

Cartesian: every combination

Cartesian mode pairs every item in List 1 with every item in List 2. Five items crossed with four items gives you 20 output lines covering all possible pairs. This grows fast: 100 items times 100 items is 10,000 lines.

Use Cartesian when you want to:

Generate all test case combinations from two parameter lists
Build a full configuration matrix
Create every possible query combination from two sets of terms

When you actually want Union, not a merge

If what you want is "everything from both lists with no duplicates," that's a Union operation, not a structural merge. The Merge Lists tool doesn't deduplicate across lists. For Union, paste both lists into the Compare Two Lists tool and copy the A Union B panel. That's the full combined set with each item appearing once.

Want to find differences instead?

Compare Two Lists shows what's only in A, only in B, in both, or in either.

Compare Two Lists →

Frequently Asked Questions

How do I combine two lists into one?

Open the Merge Lists tool, paste both lists, and choose Stack. That appends everything from List 2 below List 1. If you want duplicates removed automatically, use the Compare Two Lists tool and take the Union output instead.

How do I interleave two lists so items alternate?

Use Interleave mode in the Merge Lists tool. It alternates one item from each list: A1, B1, A2, B2. Increase the group size to take more than one item at a time before switching (A1, A2, B1, B2 etc).

How do I merge two lists without duplicates?

That is a Union operation, not a merge. Paste both lists into the Compare Two Lists tool and copy the Union output. Every unique item from either list appears exactly once.

What if my two lists have different lengths?

The Merge Lists tool gives you options: truncate to the shorter list, fill missing values with a blank, or fill with a custom default. For Stack mode the length difference doesn't matter since items are just appended.

How do I join items at the same position into one line?

Use Row Join mode. It takes the item at position 1 from each list and joins them with a separator (comma, tab, space, or custom), outputting them as one line. Good for building CSV rows from two columns of data.

What is the difference between Interleave and Row Join?

Interleave puts each item on its own separate line, alternating between lists. Row Join combines same-position items into a single line with a separator. Interleave output has twice as many lines as the inputs. Row Join output has the same number of lines as the shorter list.

How do I generate every combination of two lists?

Use Cartesian mode. It pairs every item in List 1 with every item in List 2. A list of 5 items crossed with a list of 4 items gives you 20 output lines. Useful for test data, configuration matrices, or generating all query combinations.

Can I split a merged list back apart?

Yes. The Merge Lists tool has a Split tab with reverse operations. Unshuffle reverses interleaved output. Split Columns reverses Row Join. Unstack splits on blank lines or a custom separator.