How to delete the columns of a dataframe that have only positive values in Julia?

Question

I'm working with Julia and trying to edit a DataFrame. My objective is to keep the columns in which at least one value is <=0.

For example, using the code

using DataFrames

data = Dict("A"=>[1,7,2], 
    "B"=>[3,-9,-3], 
    "C"=>[3,0,6], 
    "D"=>[8,4,2], 
    "E"=>[4,3,-4])

df = DataFrame(data)

I get the following result

And I'm trying to transform it into the following DataFrame

There are some options to remove rows based on conditions, but I haven't found any that does the same to columns.

Does anyone know how to do this in a simple way?

Answer 1

There are many ways to do this as DataFrames offers the full flexibility of Julia base, but a simple and in my opinion clear way is:

julia> data[!, any.(<=(0), eachcol(data))]
3×2 DataFrame
 Row │ B      E     
     │ Int64  Int64 
─────┼──────────────
   1 │     3      4
   2 │    -9      3
   3 │    -3     -4

Let me also add that you don't have to create a Dict to create a DataFrame, the constructor works fine with String / Vector pairs:

julia> data = DataFrame("A"=>[1,7,2], 
           "B"=>[3,-9,-3], 
           "C"=>[3,0,6], 
           "D"=>[8,4,2], 
           "E"=>[4,3,-4])
3×5 DataFrame
 Row │ A      B      C      D      E     
     │ Int64  Int64  Int64  Int64  Int64 
─────┼───────────────────────────────────
   1 │     1      3      3      8      4
   2 │     7     -9      0      4      3
   3 │     2     -3      6      2     -4