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daff: data diff

This is a library for comparing tables, producing a summary of their differences, and using such a summary as a patch file. It is optimized for comparing tables that share a common origin, in other words multiple versions of the "same" table.

For a live demo, see:

Install the library for your favorite language:

npm install daff -g  # node/javascript 
pip install daff     # python 
gem install daff     # ruby 
composer require paulfitz/daff-php  # php 
install.packages('daff') # R wrapper by Edwin de Jonge 
bower install daff   # web/javascript 

Other translations are available here:

Or use the library to view csv diffs on github via a chrome extension:

The diff format used by daff is specified here:

This library is a stripped down version of the coopy toolbox (see To compare tables from different origins, or with automatically generated IDs, or other complications, check out the coopy toolbox.

The program

You can run daff/ as a utility program:

$ daff
daff can produce and apply tabular diffs.
Call as:
  daff [--output OUTPUT.csv] a.csv b.csv
  daff [--output OUTPUT.csv] parent.csv a.csv b.csv
  daff [--output OUTPUT.ndjson] a.ndjson b.ndjson
  daff patch [--inplace] [--output OUTPUT.csv] a.csv patch.csv
  daff merge [--inplace] [--output OUTPUT.csv] parent.csv a.csv b.csv
  daff trim [--output OUTPUT.csv] source.csv
  daff render [--output OUTPUT.html] diff.csv
  daff git
  daff version
The --inplace option to patch and merge will result in modification of a.csv.
If you need more control, here is the full list of flags:
  daff diff [--output OUTPUT.csv] [--context NUM] [--all] [--act ACT] a.csv b.csv
     --context NUM: show NUM rows of context
     --all:         do not prune unchanged rows
     --act ACT:     show only a certain kind of change (update, insert, delete)
  daff diff --git path old-file old-hex old-mode new-file new-hex new-mode
     --git:         process arguments provided by git to diff drivers
  daff render [--output OUTPUT.html] [--css CSS.css] [--fragment] [--plain] diff.csv
     --css CSS.css: generate a suitable css file to go with the html
     --fragment:    generate just a html fragment rather than a page
     --plain:       do not use fancy utf8 characters to make arrows prettier

Formats supported are CSV, TSV, and ndjson.

Using with git

Run daff git csv to install daff as a diff and merge handler for *.csv files in your repository. Run daff git for instructions on doing this manually. Your CSV diffs and merges will get smarter, since git will suddenly understand about rows and columns, not just lines:

Example CSV diff

The library

You can use daff as a library from any supported language. We take here the example of Javascript. To use daff on a webpage, first include daff.js:

<script src="daff.js"></script>

Or if using node outside the browser:

var daff = require('daff');

For concreteness, assume we have two versions of a table, data1 and data2:

var data1 = [
var data2 = [

To make those tables accessible to the library, we wrap them in daff.TableView:

var table1 = new daff.TableView(data1);
var table2 = new daff.TableView(data2);

We can now compute the alignment between the rows and columns in the two tables:

var alignment = daff.compareTables(table1,table2).align();

To produce a diff from the alignment, we first need a table for the output:

var data_diff = [];
var table_diff = new daff.TableView(data_diff);

Using default options for the diff:

var flags = new daff.CompareFlags();
var highlighter = new daff.TableDiff(alignment,flags);

The diff is now in data_diff in highlighter format, see specification here:

[ [ '!', '', '+++', '' ],
  [ '@@', 'Country', 'Code', 'Capital' ],
  [ '+', 'Ireland', 'ie', 'Dublin' ],
  [ '+', 'France', 'fr', 'Paris' ],
  [ '->', 'Spain', 'es', 'Barcelona->Madrid' ],
  [ '+++', 'Germany', 'de', 'Berlin' ] ]

For visualization, you may want to convert this to a HTML table with appropriate classes on cells so you can color-code inserts, deletes, updates, etc. You can do this with:

var diff2html = new daff.DiffRender();
var table_diff_html = diff2html.html();

For 3-way differences (that is, comparing two tables given knowledge of a common ancestor) use daff.compareTables3 (give ancestor table as the first argument).

Here is how to apply that difference as a patch:

var patcher = new daff.HighlightPatch(table1,table_diff);
// table1 should now equal table2 

For other languages, you should find sample code in the packages on the Releases page.

Supported languages

The daff library is written in Haxe, which can be translated reasonably well into at least the following languages:

Some translations are done for you on the Releases page. To make another translation, or to compile from source first follow the Haxe getting started tutorial for the language you care about. At the time of writing, if you are on OSX, you should install haxe using brew install haxe --HEAD. Then do one of:

make js
make php
make py
make java
make cs
make cpp

For each language, the daff library expects to be handed an interface to tables you create, rather than creating them itself. This is to avoid inefficient copies from one format to another. You'll find a SimpleTable class you can use if you find this awkward.

Other possibilities:

API documentation


the zen of venn The [Data Commons Co-op](, "perhaps the geekiest of all cooperative organizations on the planet," has given great moral support during the development of `daff`. Donate a multiple of `42.42` in your currency to let them know you care: [](

Reading material


daff is distributed under the MIT License.