Julia：通过保留其他变量的多个值折叠DataFrame

Question

我有一些数据具有重复的字段，但我想加入一个字段。在数据中，除report以外的所有内容在每一天和每一家公司都应保持不变。公司可以在同一天提交多个报告。

我可以使用以下代码加入，但是我丢失了by函数中没有的变量。有什么建议吗？

模拟数据

using DataFrames

# Number of observations
n = 100
words = split("the wigdet drop air flat fall fling flap freeze flop tool fox", " ")
df = DataFrame(day = cumsum(rand(0:1, n)), company = rand(0:3, n), 
  report = [join(rand(words, rand(1:5, 1)[1]), " ") for i in 1:n])

x = df[:, [:day, :company]]

# Number of variables which are identical for each day/company.
nv = 100
for i in 1:nv
    df[:, Symbol("v" * string(i))] = ""
end

for i in 1:size(x, 1),j in 1:nv
    df[(df.day .== x[i,1]) .& (df.company .== x[i,2]), Symbol("v" * string(j))] = 
    join(rand('a':'z', 3), "")
end

收集的数据

outdf = by(df, [:company, :day]) do sub
  t = DataFrame(fullreport = join(sub.report, "\n(Joined)\n"))
end

Answer 1

以下是您的数据准备代码中的一些细微调整：

using DataFrames

# Number of observations
n = 100
words = split("the wigdet drop air flat fall fling flap freeze flop tool fox", " ")
df = DataFrame(day = cumsum(rand(0:1, n)), company = rand(0:3, n), 
  report = [join(rand(words, rand(1:5, 1)[1]), " ") for i in 1:n])

x = df[:, [:day, :company]]

# Number of variables which are identical for each day/company.
nv = 100
for i in 1:nv
    df[:, Symbol("v", i)] .= ""
end

for i in 1:size(x, 1), j in 1:nv
    df[(df.day .== x[i,1]) .& (df.company .== x[i,2]), Symbol("v", j)] .= join(rand('a':'z', 3), "")
end

这里是by，保留所有其他变量（假设它们在每个组中都是恒定的，即使对于较大的数据，此代码也应有效）：

outdf = by(df, [:company, :day]) do sub
    merge((fullreport = join(sub.report, "\n(Joined)\n"),),
          copy(sub[1, Not([:company, :day, :report])]))
end

我将fullreport变量作为第一个变量。

这里是将原始数据框中的所有行都保留的代码：

outdf = by(df, [:company, :day]) do sub
    insertcols!(select(sub, Not([:company, :day, :report])), 1,
                fullreport = join(sub.report, "\n(Joined)\n"))
end

现在您可以例如检查unique(outdf)产生的数据帧与拳头by产生的数据帧相同。

（（在上面的代码中，我还丢弃了:report变量，因为我想您不想在结果中使用它-对吗？）