converting dataframe with label to array in julia

Question

I have data frame with header in Julia , but I need to convert this to array for some filtering , there is some similar post that people suggest using :

iris[:, 1:3]

to get array from dataframe but this method wont work on dataframe with header , any suggestion what should I do ?

dataframe format :

FP | C1 | Cz | C2 ....
*  | *  | *  | *  ....
.  | .  | .  | .  ....
.  | .  | .  | .  ....
.  | .  | .  | .  ....

Answer 1

Have you tried convert(Matrix, iris[:,1:3])? e.g.

julia> using DataFrames

julia> df = DataFrame(a = 1:4, b = 1:4, c = randn(4), d = randn(4))
4×4 DataFrame
│ Row │ a     │ b     │ c        │ d          │
│     │ Int64 │ Int64 │ Float64  │ Float64    │
├─────┼───────┼───────┼──────────┼────────────┤
│ 1   │ 1     │ 1     │ 1.72172  │ -0.377729  │
│ 2   │ 2     │ 2     │ 0.206415 │ -0.266014  │
│ 3   │ 3     │ 3     │ 1.03785  │ -0.0317582 │
│ 4   │ 4     │ 4     │ 0.632473 │ -0.409014  │

julia> convert(Matrix, df[:,1:3])
4×3 Array{Float64,2}:
 1.0  1.0  1.72172
 2.0  2.0  0.206415
 3.0  3.0  1.03785
 4.0  4.0  0.632473

Answer 2

The accepted answer does a good job of answering the question as stated.

If your only reason for wanting to convert the DataFrame to an Array is to filter it, though, it may be worth looking into the methods available for filtering DataFrame objects directly. See, for some examples, https://dataframesjl.readthedocs.io/en/latest/subsets.html and https://dataframesjl.readthedocs.io/en/latest/split_apply_combine.html.

(Sorry in advance if this is better suited for a comment than an answer—not enough reputation to comment on here yet.)