Replace specific values in Julia Dataframe column with random value-CodePudding

I'm looking for a way to replace values in Dataframe column with random numbers. They should be different in every row where the substitution was performed.

For example replacing "X" with random numbers drawn from 100:120 range

julia> df = DataFrame(:a=>[1,2,"X","X",5,"X"],)
6×1 DataFrame
│ Row │ a   │
│     │ Any │
├─────┼─────┤
│ 1   │ 1   │
│ 2   │ 2   │
│ 3   │ X   │
│ 4   │ X   │
│ 5   │ 5   │
│ 6   │ X   │

* Replacing X with random values in 100:120 *

julia> df
6×1 DataFrame
│ Row │ a   │
│     │ Any │
├─────┼─────┤
│ 1   │ 1   │
│ 2   │ 2   │
│ 3   │ 103 │
│ 4   │ 110 │
│ 5   │ 5   │
│ 6   │ 116 │

I've tried using replace but rand is evaluated before replace:

julia> replace!(df.a,"X"=> rand(100:120))
julia> df
6×1 DataFrame
│ Row │ a   │
│     │ Any │
├─────┼─────┤
│ 1   │ 1   │
│ 2   │ 2   │
│ 3   │ 115 │
│ 4   │ 115 │
│ 5   │ 5   │
│ 6   │ 115 │

CodePudding user response：

A one liner could be:

replace!( x-> x=="X" ? rand() : x, df.a)

CodePudding user response：

Alternatively using operation specification syntax:

transform!(df, :a => ByRow(a -> a == "X" ? rand() : a)=> :a)

or you can do:

rand!(view(df.a, df.a .== "X"), Float64)

for another in-place approach (but replace! will likely be more efficient)