# Where are the docs for the DataFrames by() function

**URL:** <https://discourse.julialang.org/t/where-are-the-docs-for-the-dataframes-by-function/1775>\
**Category:** General Usage\
**Created:** [January 29, 2017, 10:08pm UTC](https://discourse.julialang.org/t/where-are-the-docs-for-the-dataframes-by-function/1775 "2017-01-29T22:08:29Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![DWSchulze](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dwschulze/32/35968_2.png) [@DWSchulze](https://discourse.julialang.org/u/DWSchulze)\
**Post date:** [January 29, 2017, 10:08pm UTC](https://discourse.julialang.org/t/where-are-the-docs-for-the-dataframes-by-function/1775/1 "2017-01-29T22:08:29Z")

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I can’t find any docs for the by() function in DataFrames. There is an example of usage here, but no docs:

[http://dataframesjl.readthedocs.io/en/latest/reshaping\_and\_pivoting.html?highlight=by](http://dataframesjl.readthedocs.io/en/latest/reshaping_and_pivoting.html?highlight=by)

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**Author:** ![tshort](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tshort/32/43_2.png) [@tshort](https://discourse.julialang.org/u/tshort)\
**Post date:** [January 29, 2017, 10:20pm UTC](https://discourse.julialang.org/t/where-are-the-docs-for-the-dataframes-by-function/1775/2 "2017-01-29T22:20:10Z")

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At the REPL, `?by` works for me.

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**Author:** ![DWSchulze](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dwschulze/32/35968_2.png) [@DWSchulze](https://discourse.julialang.org/u/DWSchulze)\
**Post date:** [January 29, 2017, 11:13pm UTC](https://discourse.julialang.org/t/where-are-the-docs-for-the-dataframes-by-function/1775/3 "2017-01-29T23:13:56Z")

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I guess the REPL is the only documentation. The REPL showed this which was helpful:

by(d, cols, f) is equivalent to combine(map(f, groupby(d, cols)))

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<div class="post-metadata">

**Author:** ![DWSchulze](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dwschulze/32/35968_2.png) [@DWSchulze](https://discourse.julialang.org/u/DWSchulze)\
**Post date:** [January 29, 2017, 11:21pm UTC](https://discourse.julialang.org/t/where-are-the-docs-for-the-dataframes-by-function/1775/4 "2017-01-29T23:21:55Z")

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Found this while searching for the DataFrames.nrow function:

[https://en.wikibooks.org/wiki/Introducing\_Julia/DataFrames](https://en.wikibooks.org/wiki/Introducing_Julia/DataFrames)