daff

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:

http://paulfitz.github.com/daff/

Get the core library for your preferred language here:

https://github.com/paulfitz/daff/releases

Or with node:

npm install daff

Or with pip:

pip3 install daff  # currently needs python3

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

https://github.com/theodi/csvhub

The diff format used by daff is specified here:

http://dataprotocols.org/tabular-diff-format/

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

The program

There is a commandline utility wrapping the core functions of the library:

$ 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.jsonbook] a.jsonbook b.jsonbook
  daff patch [--output OUTPUT.csv] source.csv patch.csv
  daff trim [--output OUTPUT.csv] source.csv
  daff render [--output OUTPUT.html] diff.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 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

The library

To use this library from Javascript, first include daff.js on a webpage:

<script src="daff.js"></script>

Or with nodejs:

var daff = require('daff');

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

var data1 = [
    ['Country','Capital'],
    ['Ireland','Dublin'],
    ['France','Paris'],
    ['Spain','Barcelona']
];
var data2 = [
    ['Country','Code','Capital'],
    ['Ireland','ie','Dublin'],
    ['France','fr','Paris'],
    ['Spain','es','Madrid'],
    ['Germany','de','Berlin']
];

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);
highlighter.hilite(table_diff);

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

http://share.find.coop/doc/spec_hilite.html

[ [ '!', '', '+++', '' ],
  [ '@@', '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();
diff2html.render(table_diff);
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);
patcher.apply();
// table1 should now equal table2

Other languages

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

• Javascript
• PHP
• Python
• Java
• C#
• C++

The Javascript translation is available via npm. PHP and C++ translations are posted on the Releases page. To make another translation, follow the Haxe getting started tutorial for the language you care about, then do one of:

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

@Floppy has made a lovingly-hand-written native Ruby port that covers core functionality. I've made a brutally-machine-converted Ruby port that is a full translation but may include utter gibberish.

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.

Reading material

• http://dataprotocols.org/tabular-diff-format/ : a specification of the diff format we use.
• http://theodi.org/blog/csvhub-github-diffs-for-csv-files : using this library with github.
• http://theodi.org/blog/adapting-git-simple-data : using this library with gitlab.
• http://okfnlabs.org/blog/2013/08/08/diffing-and-patching-data.html : a summary of where the library came from.
• http://blog.okfn.org/2013/07/02/git-and-github-for-data/ : a post about storing small data in git/github.
• http://blog.ouseful.info/2013/08/27/diff-or-chop-github-csv-data-files-and-openrefine/ : counterpoint - a post discussing tracked-changes rather than diffs.

License

daff is distributed under the MIT License.