英文:
Sum of Julia Dataframe column where values of another column are in a list
问题
如何编写适用于Julia的一行代码，用于对“col1”中的值在“list”中的行的“col2”值求和？我对Julia还不太熟悉，尝试以下代码会出现错误“Exception has occurred: DimensionMismatch DimensionMismatch: arrays could not be broadcast to a common size; got a dimension with lengths 10 and 3”
total_sum = sum(df[ismember(df[:, :col1], list), :col2])
英文:
How do I make a line of code that works for Julia to sum the values of col2 where the values of col1 that are in list ? I'm pretty new to Julia and trying the following lines prints out the error Exception has occurred: DimensionMismatch
DimensionMismatch: arrays could not be broadcast to a common size; got a dimension with lengths 10 and 3
total_sum = sum(df[ismember(df[:, :col1], list), :col2])
答案1
得分: 2
以下是已翻译的代码部分：
julia> df = DataFrame(reshape(1:12,4,3),:auto)
4×3 DataFrame
Row │ x1 x2 x3
│ Int64 Int64 Int64
─────┼─────────────────────
1 │ 1 5 9
2 │ 2 6 10
3 │ 3 7 11
4 │ 4 8 12
julia> list = [2,3]
2-element Vector{Int64}:
2
3
julia> sum(df.x2[df.x1 .∈ Ref(list)])
13
此代码段使用了 Julia 中的广播功能，在其中 in（Julia 中的 ismember 函数）也可以写为 ∈。Ref(list) 用于防止对 list 进行广播。
英文:
One way could be:
julia> df = DataFrame(reshape(1:12,4,3),:auto)
4×3 DataFrame
Row │ x1 x2 x3
│ Int64 Int64 Int64
─────┼─────────────────────
1 │ 1 5 9
2 │ 2 6 10
3 │ 3 7 11
4 │ 4 8 12
julia> list = [2,3]
2-element Vector{Int64}:
2
3
julia> sum(df.x2[df.x1 .∈ Ref(list)])
13
Uses broadcasting on in (how ismember is written in Julia) which can also be written as ∈. Ref(list) is used to prevent broadcasting over list.
答案2
得分: 1
filter! 是一个值得了解的函数，具体取决于你想要做什么（使用 Dan Getz 的代码示例）：
julia> sum(filter!(:x1 => x1 -> x1 ∈ [2,3], df).x2)
13
英文:
Depending on what you want to do filter! is also worth knowing (using code form Dan Getz's answer):
julia> sum(filter!(:x1 => x1 -> x1 ∈ [2,3], df).x2)
13
答案3
得分: 0
Not exactly sure if this is what you're asking but try intersect
julia> using DataFrames
julia> df = DataFrame(a = 1:5, b = 2:6)
5×2 DataFrame
Row │ a b
│ Int64 Int64
─────┼──────────────
1 │ 1 2
2 │ 2 3
3 │ 3 4
4 │ 4 5
5 │ 5 6
julia> list = collect(3:10);
julia> sum(df.b[intersect(df.a, list)])
15
英文:
Not exactly sure if this is what you're asking but try intersect
julia> using DataFrames
julia> df = DataFrame(a = 1:5, b = 2:6)
5×2 DataFrame
Row │ a b
│ Int64 Int64
─────┼──────────────
1 │ 1 2
2 │ 2 3
3 │ 3 4
4 │ 4 5
5 │ 5 6
julia> list = collect(3:10);
julia> sum(df.b[intersect(df.a, list)])
15
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