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ListDiff

Compare list basics

Last updated: 2026-08-02

ListDiff compares unique values after cleanup—trim spaces, skip blank lines, optional dedupe, and optional splitting when one line holds several values.

Numbers look wrong? It’s usually spaces, capitals, blank lines, or how CSV was read—not the compare logic itself. This page explains what each result means.

Core terms (plain language)

  • Item: one thing you compare—usually one line, unless you split a line into several values.
  • Key: the cleaned value used for matching (affected by case, trim, and blank-line settings).
  • Text lines: how many lines are in the box, including blanks.
  • Raw lines: how many items remain after your current settings (skip blanks, split, trim).

Who this page is for

  • Anyone who wants to know what A only / Intersection really mean.
  • People comparing expected vs actual lists from spreadsheets or CSV.
  • Anyone chasing odd counts after pasting from Excel or Instagram downloads.

A only

Items that appear in List A but not in List B.

B only

Items that appear in List B but not in List A.

Intersection

Items that appear in both lists.

Union

All unique items that appear in either list.

Symmetric difference

Items that appear in exactly one of the two lists (A-only plus B-only).

Duplicates within a list

These tabs highlight keys that occur more than once on a side before set collapsing rules remove duplicates—useful when your source data accidentally repeats entries.

Stats panel meaning

  • Keys: A / B: unique normalized keys used for set operations.
  • Raw lines: A / B: processed item count under current options. This can differ from the “lines” badge above each input.

How to diagnose surprising results

  1. Start with Case sensitive and Ignore leading/trailing spaces.
  2. Check whether blank lines should be considered data or noise.
  3. If source lines contain multiple values, verify split delimiters.
  4. For CSV imports, confirm row-vs-first-column mode and header handling.

Example

List A: Apple, banana
List B: apple, banana
Setting: case sensitive off
Result: both lists match on those items; A only and B only are empty.

How settings change the result

  • Case sensitive off + trim spaces on usually finds more matches.
  • Skip blank lines on lowers the processed count, but the line counter above the box still counts blanks.
  • Split on can turn one messy pasted line into many items—counts jump.
  • Dedupe on compares unique values; leave it off first if you want to see repeats.

Reading the numbers

  • If A only is high and B only is low, A may have extras (or B is incomplete).
  • If both sides show lots of “only” items, the two lists may not be the same kind of value.
  • If duplicates in A are high, clean repeats before you trust the missing list.

What the home-page controls do

Quick reference for buttons and toggles on the compare tool. Start here if you’re unsure what a control changes.

Input header (per side)

  • XX lines: text line count in that input box, including blank lines.
  • Import .txt/.csv: import local file text into current side (browser-local, no server-side compare processing).
  • CSV controls: shown only after CSV import; choose row mode vs first column and optional header skipping.
  • Example (page header): loads a built-in preset and runs compare automatically.
  • Clear all (page header): resets both lists, options, and results to defaults.

Input action buttons (per side)

  • Copy: copy current input text for that side.
  • Clear: clear this side’s input content.
  • Sort: sort lines lexicographically (en-US locale behavior).
  • Trim lines: trim leading/trailing spaces on each line only.
  • Dedupe lines: remove duplicate lines while keeping first-seen order.

Split settings (per side)

  • Split long lines: split one line into multiple items using selected delimiters.
  • Chevron icon: expand/collapse split details panel (manual control).
  • Delimiter buttons: multi-select delimiters; supports English and Chinese punctuation plus tab: , ， ; ； : ： \t.
  • Collapsed summary: shows enabled/disabled state and number of configured delimiters.

Global options card

  • Case sensitive: ON means Apple and apple are different keys.
  • Ignore leading/trailing spaces: trims around each item before key comparison.
  • Ignore empty lines: removes blank lines from processed compare items.
  • Dedupe items (set keys): collapses repeated keys before set comparison.

Compare and results actions

  • Compare lists: run compare with current input + option state.
  • Result tabs: A only / B only / Intersection / Union / Symmetric Δ / Dupes in A / Dupes in B.
  • Copy in results: copy all lines from the active tab.
  • Download .txt: export active tab as plain text (one item per line).
  • Download .csv: export active tab as single-column CSV for spreadsheet import.

Related content

Related guides: Excel paste tips, export to Excel, and compare two local files.

Related reading

FAQ

Why can line counts and key counts differ?
Line count is raw textarea lines. Key count is normalized unique compare keys.

Should I always enable dedupe items?
Not always. Keep it OFF when you need duplicate-aware diagnostics, then re-run with ON for final set outputs.

Can I compare mixed IDs and text labels?
Yes, but keep normalization options stable across both sides to avoid false mismatches.

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