Error in chaining two consecutive @count

[danlooo]

I want to count the number of groups having the same number of elements. In R, this can be archived using a consecutive call of count:

library(dplyr)
df <- tibble(id=1:10, group = c(1,1,1,1,1,2,2,2,2,2))
df |>
  count(group) |>
  count(n)
#> Storing counts in `nn`, as `n` already present in input
#> ℹ Use `name = "new_name"` to pick a new name.
#> # A tibble: 1 × 2
#>       n    nn
#>   <int> <int>
#> 1     5     2

Indeed, there are 2 groups having 5 elements each. However, this can not be archived with Tidier.jl:

using Tidier
df = DataFrame(id=1:10,group=[1,1,1,1,1,2,2,2,2,2])
@chain df begin
    @count(group)
    @count(n)
end
# ERROR: ArgumentError: column :n in returned data frame is not equal to grouping key :n
# Stacktrace:
#  [1] _combine_prepare_norm(gd::DataFrames.GroupedDataFrame{DataFrame}, cs_vec::Vector{Any}, keepkeys::Bool, ungroup::Bool, copycols::Bool, keeprows::Bool, renamecols::Bool, threads::Bool)
#    @ DataFrames ~/.julia/packages/DataFrames/58MUJ/src/groupeddataframe/splitapplycombine.jl:104
#  [2] _combine_prepare(gd::DataFrames.GroupedDataFrame{DataFrame}, ::Base.RefValue{Any}; keepkeys::Bool, ungroup::Bool, copycols::Bool, keeprows::Bool, renamecols::Bool, threads::Bool)
#    @ DataFrames ~/.julia/packages/DataFrames/58MUJ/src/groupeddataframe/splitapplycombine.jl:52
#  [3] _combine_prepare
#    @ ~/.julia/packages/DataFrames/58MUJ/src/groupeddataframe/splitapplycombine.jl:26 [inlined]
#  [4] combine(gd::DataFrames.GroupedDataFrame{DataFrame}, args::Union{Regex, AbstractString, Function, Signed, Symbol, Unsigned, Pair, Type, DataAPI.All, Between, Cols, InvertedIndices.InvertedIndex, AbstractVecOrMat}; keepkeys::Bool, ungroup::Bool, renamecols::Bool, threads::Bool)
#    @ DataFrames ~/.julia/packages/DataFrames/58MUJ/src/groupeddataframe/splitapplycombine.jl:861
#  [5] macro expansion
#    @ ~/.julia/packages/TidierData/hI0Pq/src/TidierData.jl:324 [inlined]
#  [6] top-level scope
#    @ REPL[3]:70

[kdpsingh]

This is fixable. We need to check whether n (and nn, etc) already exists before deciding on the new variable name containing the count.

[kdpsingh]

Moved this issue to the TidierData.jl package because Tidier.jl is a meta-package.