I recently updated my DataFrames.jl package and noticed the following deprecation warning when doing df[:a]: Warning: `getindex(df::DataFrame, col_ind::ColumnIndex)` is deprecated, use `df[!, col_ind]` instead. I understand that I need to start doing the above as df[:, :a] or df[!, :a] but is ther…

First make a copy, second is a view, no?

That sounds like it’s probably right, but I don’t know how to check :slightly_smiling_face: I think this might show that you are right: using DataFrames df = DataFrame([collect(1:10), collect(11:20)], [:a, :b]) julia> df[:, :a] === df[:, :a] false julia> df[!, :a] === df[!, :a] true In the fir…

Indeed. You can also use @time and look for allocations. julia> @time df[:, :x1]; 0.000004 seconds (5 allocations: 256 bytes) julia> @time df[!, :x1]; 0.000003 seconds (4 allocations: 160 bytes) or use BenchmarkTools: julia> using BenchmarkTools julia> @btime df[:, :x1]; 57.682 ns (1 allo…

I didn’t even realize that you can just do df.a :laughing: That’s so much nicer than df[!, :a]

Note, this works for everything except assigning a single value to a non-existent column. That is: julia> df = DataFrame(a=rand(10)); julia> df.b = rand(10); julia> df.c = ["blah" for _ in 1:10]; julia> df.c .= "foo"; julia> df.d .= "bar"; ERROR: ArgumentError: column name :d not found in the d…

Difference between df[:, :a] and df[!, :a]

General Usage

stevengj Split this topic January 18, 2023, 9:26pm 8

2 posts were split to a new topic: Copy vs view of DataFrame column?

Topic		Replies	Views
Copy vs view of DataFrame column? General Usage dataframes	16	1014	January 19, 2023
! vs @view for indexing DataFrame Data dataframes	5	421	October 29, 2022
Indexing DataFrame with : does not generate a copy Specific Domains dataframes	2	800	March 17, 2022
Different of df[!, :name] and df[:, :name] New to Julia dataframes	3	208	May 12, 2023
Difference between df.column and df[!, :column] New to Julia question , dataframes	9	2904	July 23, 2020

Difference between df[:, :a] and df[!, :a]

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