2020-11-19-225744.jl

# julia> versioninfo()
# Julia Version 1.5.0
# Commit 96786e22cc (2020-08-01 23:44 UTC)
# Platform Info:
#   OS: macOS (x86_64-apple-darwin18.7.0)
#   CPU: Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
#   WORD_SIZE: 64
#   LIBM: libopenlibm
#   LLVM: libLLVM-9.0.1 (ORCJIT, skylake)

using BenchmarkTools
using DataFrames
using StatsBase
using Random
Random.seed!(0)
nrow = 100
ncol = 400_000
df = DataFrame(sample([-1,0,1], (nrow, ncol)))

"""
    jl_mode(df::DataFrame)

各列の最頻値を返す
Python版のオリジナル: https://twitter.com/nkay/status/1328231713919496194
"""
function jl_mode(df)
    arr=convert(Matrix,df)
    maxvalue, minvalue, ncol = maximum(arr), minimum(arr), size(arr,2)
    offset = collect(1:ncol) .* (maxvalue-minvalue+1) .- minvalue
    return argmax.(eachcol(reshape(counts(arr .+ offset'), :, ncol))) .+ (minvalue - 1)
end

@btime jl_mode(df);
# 346.782 ms (400026 allocations: 653.08 MiB)

# StatsBase.mode()を使った場合
@btime mapcols(mode, df);
# 895.601 ms (2399604 allocations: 333.43 MiB)

Python ver. : https://gist.github.com/a3b8343ea37f5bbc2c2ecc95390e9edb