daff 1.1.6

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

Download the code for your preferred language here:
> https://github.com/paulfitz/daff/releases

For certain languages you can use the command-line:
````sh
npm install daff -g # node/javascript
pip3 install daff # python3
gem install daff # ruby
````

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
-----------

You can run `daff`/`daff.py`/`daff.rb` 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.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
````

Using with git
--------------

Run `daff git csv` to see how to use daff to improve `git`'s handling
of csv files.

````
$ daff git csv
You can use daff to improve git's handling of csv files, by using it as a
diff driver (for showing what has changed) and as a merge driver (for merging
changes between multiple versions). Here is how.

Create and add a file called .gitattributes in the root directory of your
repository, containing:

*.csv diff=daff-diff
*.csv merge=daff-merge

Create a file called .gitconfig in your home directory (or alternatively
open .git/config for a particular repository) and add:

[merge "daff-merge"]
name = daff tabular merge
driver = daff merge --output %A %O %A %B

[diff "daff-diff"]
command = daff diff --git

Make sure you can run daff from the command-line as just "daff" - if not,
replace "daff" in the driver and command lines above with the correct way
to call it.
````

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`:
```html
<script src="daff.js"></script>
```
Or if using node outside the browser:
```js
var daff = require('daff');
```

For concreteness, assume we have two versions of a table,
`data1` and `data2`:
```js
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`:
```js
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:
```js
var alignment = daff.compareTables(table1,table2).align();
```

To produce a diff from the alignment, we first need a table
for the output:
```js
var data_diff = [];
var table_diff = new daff.TableView(data_diff);
```

Using default options for the diff:
```js
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

```js
[ [ '!', '', '+++', '' ],
[ '@@', '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:
```js
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:
```js
var patcher = new daff.HighlightPatch(table1,table_diff);
patcher.apply();
// table1 should now equal table2
```

For other languages, you should find sample code in
the packages on the [Releases](https://github.com/paulfitz/daff/releases) page.


Supported languages
-------------------

The `daff` library is written in [Haxe](http://haxe.org/), which
can be translated reasonably well into at least the following languages:

* Javascript
* PHP
* Python
* Java
* C#
* C++
* (via a hack, just for `daff`) Ruby

Some translations are done for you on the
[Releases](https://github.com/paulfitz/daff/releases) page.
To make another translation,
follow the
[Haxe getting started tutorial](http://haxe.org/doc/start) for the
language you care about, then do one of:

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

[@Floppy](https://github.com/Floppy) has made a lovingly-hand-written [native Ruby port](https://github.com/theodi/coopy-ruby) that covers core functionality. I've made a brutally-machine-converted port that is a full translation but less idiomatic.

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.