Duplicate Line RemoverFree online other calculator — instant results, no sign-up
Remove repeated lines while preserving first occurrence order.
Sign in to save results and favorites.
About the Duplicate Line Remover
The Duplicate Line Remover removes repeated lines from text while keeping the first occurrence of each line in its original order. It works on whole lines rather than individual words or sentences. With the default text, "Hello world. This is a sample.", the Unique lines output is unchanged.
- Text
- The text to check for repeated lines, entered as plain text with line breaks separating entries; it has no measurement units.
Formula and method
U = join_newlines([L_i | 1 ≤ i ≤ n and L_i ≠ L_j for every j < i]); for Text = "Hello world. This is a sample.", Unique lines = Hello world. This is a sample.
- L_iThe line at position i in the input text.
- L_jAn earlier line at position j, used to check whether the current line has already appeared.
- i, jLine positions in the original input, with j < i indicating an earlier position.
- nThe total number of input lines.
- UThe Unique lines output: retained lines joined with line breaks in their original order.
- join_newlinesThe operation that combines retained lines into text with a line break between adjacent lines.
Split the input text into lines and scan them from top to bottom. Keep a record of lines already encountered: retain a line when it first appears and skip any later matching occurrence. Join the retained lines in encounter order. The default input, "Hello world. This is a sample.", is a single line with no repeated occurrence, so it is retained unchanged.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- TextHello world. This is a sample.
Results
- Unique linesHello world. This is a sample.
How to use the Duplicate Line Remover
- 1Enter or paste your content into Text, placing each entry on its own line.
- 2Check that the line breaks represent the entries you want compared; visual wrapping is not necessarily a line break.
- 3Run the Duplicate Line Remover to discard later occurrences of matching lines.
- 4Read the Unique lines output and confirm that the first occurrence order is preserved.
- 5Copy the result for reuse, keeping the original text if you may need the removed repetitions.
Reading your result
The output row labeled Unique lines contains the text remaining after repeated lines are removed. Each retained line appears where its first occurrence belongs relative to the other retained lines; the output is not alphabetically sorted. For the default input, the row reads: Unique lines = Hello world. This is a sample.
Limitations
The formula describes exact whole-line matching; case folding, whitespace trimming, and other normalization are not specified for this tool and should not be assumed. Lines that differ in capitalization, spaces, or punctuation may therefore remain separate. Repeated words or sentences within a line are not removed. Blank-line handling and preservation of trailing line breaks are not specified, so inspect the result when formatting matters.
Common questions
Does the Duplicate Line Remover sort the remaining lines?+
No. It preserves the order of first occurrence, so an earlier unique line stays ahead of unique lines first encountered later.
Why does the default text remain unchanged?+
"Hello world. This is a sample." is a single input line with no later duplicate. The Unique lines output is therefore Hello world. This is a sample.
Will it remove repeated words within a line?+
No. The comparison unit is an entire line, so repetition inside an otherwise retained line is left intact.
Why might two similar-looking lines both remain?+
They may differ in capitalization, punctuation, or invisible whitespace. The tool does not specify normalization options, so do not assume these differences are ignored.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
You might also like
Word Counter
Count whitespace-separated words.
Character Counter
Count Unicode code points with and without whitespace.
Sentence Counter
Estimate sentences using terminal punctuation.
Line Counter
Count logical lines, including a trailing empty line.
Text Reverser
Reverse the order of Unicode code points.
Text Palindrome Checker
Check a palindrome while ignoring punctuation and letter case.
Results are estimates for informational purposes and are not financial, medical or legal advice.