# How to properly plot DataFrames? (... and simplify my call to violin in StatPlots.)

**URL:** <https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509>\
**Category:** Visualization\
**Tags:** question, plotting\
**Created:** [August 15, 2018, 3:18pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509 "2018-08-15T15:18:34Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![rickhg12hs](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rickhg12hs/32/5926_2.png) [@rickhg12hs](https://discourse.julialang.org/u/rickhg12hs)\
**Post date:** [August 15, 2018, 3:18pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/1 "2018-08-15T15:18:34Z")

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I’m looking for a more concise way to call `violin`. I just want a violin of each category/column of data and also have all the labeling consistent with the `Dataframe` names.

```julia
# some data to play with
n = 10000
f(k) = randn(k)
df2 = DataFrame(hcat(f(n).+1, f(n).-1, 2*f(n), 0.5*f(n)-3, 2*f(n).^2, abs.(f(n))),
    map(num->Symbol("Set",num),4:9));
# Now plot a violin of each "Set" on the same graph
violin(hcat(convert(Vector{String}, df2.colindex.names)...),
    hcat(df2.columns...),
    labels=df2.colindex.names,
    trim=false)

```

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**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [August 15, 2018, 4:20pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/2 "2018-08-15T16:20:02Z")

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I think this an error where the plot commands wants the labels to match the dimensions of the data. Since your data is concatated horizontally, its wants the labels to be a row vector. Try `reshape(df2.colindex.names. :, 1)`, or better yet `reshape(named(df), :, 1)`.

There is a PR out there to have labels accept regular vectors but I can’t find it at the moment.

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**Author:** ![ValdarT](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/valdart/32/24146_2.png) [@ValdarT](https://discourse.julialang.org/u/ValdarT)\
**Post date:** [August 15, 2018, 7:42pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/3 "2018-08-15T19:42:20Z")

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Usually you would use the `@df` macro to work with `DataFrames` but this assumes a different (‘long’) data format. In your case I would do

```julia
violin(convert(Matrix, df2), xticks=(1:ncol(df2), names(df2)), legend=false)

```

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**Author:** ![rickhg12hs](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rickhg12hs/32/5926_2.png) [@rickhg12hs](https://discourse.julialang.org/u/rickhg12hs)\
**Post date:** [August 15, 2018, 8:02pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/4 "2018-08-15T20:02:03Z")

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Thanks! This does produce the desired plot!

Is the “long” data format `stack(df2)`? If so, how would I use `@df`? I’ve tried various `@df` incantations that either spit out errors or didn’t make the plot I want.

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**Author:** ![piever](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/piever/32/1815_2.png) [@piever](https://discourse.julialang.org/u/piever)\
**Post date:** [August 15, 2018, 8:16pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/5 "2018-08-15T20:16:59Z")

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To pass to the long format that’s needed for a violin plot you can simply use `stack`, e.g.

```julia
df2 |> stack |> @df violin(:variable, :value)

```

You can look at the result of `stack(df2)` to see what “long format” refers to.

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**Author:** ![rickhg12hs](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rickhg12hs/32/5926_2.png) [@rickhg12hs](https://discourse.julialang.org/u/rickhg12hs)\
**Post date:** [August 15, 2018, 8:23pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/6 "2018-08-15T20:23:06Z")

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I tried that, but I get an error:

```julia
No user recipe defined for Symbol

Stacktrace:
 [1] copy!(::Array{Any,1}, ::Base.Generator{Array{Symbol,1},Plots.##223#225{Dict{Symbol,Any}}}) at ./abstractarray.jl:573
 [2] convertToAnyVector(::Array{Symbol,1}, ::Dict{Symbol,Any}) at /home/rick/.julia/v0.6/Plots/src/series.jl:58
 [3] macro expansion at /home/rick/.julia/v0.6/Plots/src/series.jl:131 [inlined]
 [4] apply_recipe(::Dict{Symbol,Any}, ::Type{Plots.SliceIt}, ::Array{Symbol,1}, ::Array{Float64,1}, ::Void) at /home/rick/.julia/v0.6/RecipesBase/src/RecipesBase.jl:291
 [5] _process_userrecipes(::Plots.Plot{Plots.GRBackend}, ::Dict{Symbol,Any}, ::Tuple{Array{Symbol,1},Array{Float64,1}}) at /home/rick/.julia/v0.6/Plots/src/pipeline.jl:81
 [6] _plot!(::Plots.Plot{Plots.GRBackend}, ::Dict{Symbol,Any}, ::Tuple{Array{Symbol,1},Array{Float64,1}}) at /home/rick/.julia/v0.6/Plots/src/plot.jl:179
 [7] #plot#212(::Array{Any,1}, ::Function, ::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/Plots/src/plot.jl:58
 [8] (::RecipesBase.#kw##plot)(::Array{Any,1}, ::RecipesBase.#plot, ::Array{Symbol,1}, ::Array{Float64,1}, ::Vararg{Array{Float64,1},N} where N) at ./<missing>:0
 [9] #violin#766(::Array{Any,1}, ::Function, ::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/RecipesBase/src/RecipesBase.jl:385
 [10] violin(::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/RecipesBase/src/RecipesBase.jl:385
 [11] #add_label#15(::Array{Any,1}, ::Function, ::Array{String,1}, ::Function, ::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/StatPlots/src/df.jl:129
 [12] (::##75#76)(::DataFrames.DataFrame) at ./<missing>:0
 [13] |>(::DataFrames.DataFrame, ::##75#76) at ./operators.jl:862
 [14] include_string(::String, ::String) at ./loading.jl:522

```

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<div class="post-metadata">

**Author:** ![piever](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/piever/32/1815_2.png) [@piever](https://discourse.julialang.org/u/piever)\
**Post date:** [August 15, 2018, 8:36pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/7 "2018-08-15T20:36:15Z")

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Somehow I think that should work though, could you open an issue over at StatPlots?

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<div class="post-metadata">

**Author:** ![piever](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/piever/32/1815_2.png) [@piever](https://discourse.julialang.org/u/piever)\
**Post date:** [August 15, 2018, 9:18pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/8 "2018-08-15T21:18:25Z")

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Btw, to be practical, the best option to use `@df` here is with `cols` that allows you to select a few columns (`cols(1:2)` selects the first two, `cols()` selects all of them, etc…).

So in this case:

`@df df2 violin(cols())`

or for example:

`@df df2 violin(cols(1:3))`

If you only want some columns.

The other method via `stack` requires you to manually convert one column from `Symbol` to `String` (which I believe is not ideal, Plots should take care of that automatically):

```julia
df2 |> stack |> @df violin(string.(:variable), :value)

```

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<div class="post-metadata">

**Author:** ![rickhg12hs](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rickhg12hs/32/5926_2.png) [@rickhg12hs](https://discourse.julialang.org/u/rickhg12hs)\
**Post date:** [August 16, 2018, 4:19pm UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/9 "2018-08-16T16:19:22Z")

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Thanks! To get the x-axis labels I want, is this the best way?

```julia
@df df2 violin(cols(),xticks=(1:ncol(df2), names(df2)))

```

Also, `df2 |> stack |> @df violin(string.(:variable), :value)` only plots in one color and the legend shows only one item.

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**Author:** ![piever](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/piever/32/1815_2.png) [@piever](https://discourse.julialang.org/u/piever)\
**Post date:** [August 17, 2018, 10:52am UTC](https://discourse.julialang.org/t/how-to-properly-plot-dataframes-and-simplify-my-call-to-violin-in-statplots/13509/10 "2018-08-17T10:52:48Z")

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> Thanks! To get the x-axis labels I want, is this the best way?
> 
> ```julia
> @df df2 violin(cols(),xticks=(1:ncol(df2), names(df2)))
> 
> ```

Yes, I think that’s it, though I’m not sure why Plots would give you a numeric x axis by default.