I just found this package FreqTables, which allows one to easily construct frequency tables from DataFrames (I'm using DataFrames.jl).
The following lines of code return me a frequency table:
df = CSV.read("exampledata.csv")
freqtable(df,:col_name)
My question is how to turn the output into a dataframe again. The output from the frequency table function seems to be a NamedArray, which I haven't been able turn into a dataframe.
This does not directly answer your question, but freq tables you can alternatively just write:
julia> df = DataFrame(A = [2,2,2,2,5,5,5])
7×1 DataFrame
│ Row │ A │
│ │ Int64 │
├─────┼───────┤
│ 1 │ 2 │
│ 2 │ 2 │
│ 3 │ 2 │
│ 4 │ 2 │
│ 5 │ 5 │
│ 6 │ 5 │
│ 7 │ 5 │
julia> combine(groupby(df, :A), nrow => :Freq)
2×2 DataFrame
│ Row │ A │ Freq │
│ │ Int64 │ Int64 │
├─────┼───────┼───────┤
│ 1 │ 2 │ 4 │
│ 2 │ 5 │ 3 │
to get the same
I found this solution to work for me:
using DataFrames, FreqTables
ft = freqtable(df, :A)
df = DataFrame(A = [2,2,2,2,5,5,5], B = [1,1,1,6,6,6,6])
DataFrame(A = names(ft)[1], Freq = ft)
Result:
2×2 DataFrame
│ Row │ A │ Freq │
│ │ Int64 │ Int64 │
├─────┼───────┼───────┤
│ 1 │ 2 │ 4 │
│ 2 │ 5 │ 3 │