如何“取消列出" data.table 中的列 [英] How to 'unlist' a column in a data.table

问题描述

在我的表格中，一些单元格是向量而不是单个值，即列是列表而不是向量:

dt1 <- data.table(colA= c('A1','A2','A3'),colB=list('B1',c('B2a','B2b'),'B3'),colC= c('C1','C2','C3'),冷= c('D1','D2','D3'))dt1# colA colB colC colD#1:A1 B1 C1 D1#2:A2 B2a，B2b C2 D2#3:A3 B3 C3 D3

我需要将其重新整形为长格式，不列出该列 colB.到目前为止，我是这样做的:

dt1[,.(colB=unlist(colB)),by=.(colA,colC,colD)]# colA colC colD colB#1:A1 C1 D1 B1#2:A2 C2 D2 B2a#3:A2 C2 D2 B2b#4:A3 C3 D3 B3

它可以完成这项工作，但我不喜欢我必须在 by= 中明确指出所有其他列名.有没有更好的方法来做到这一点?
(我确定它已经在其他地方得到了回答，但我目前找不到)

附:理想情况下，我想在没有任何外部包的情况下进行管理

解决方案

将我的评论提升为答案.使用:

dt1[,.(colB = unlist(colB)), by = setdiff(names(dt1), 'colB')]

给予:

<块引用>

 colA colC colD colB1:A1 C1 D1 B12:A2 C2 D2 B2a3:A2 C2 D2 B2b4:A3 C3 D3 B3

或者作为替代方案(@Frank 的提议略有不同):

dt1[rep(dt1[,.I], lengths(colB))][, colB := unlist(dt1$colB)][]

in my table, some cells are vectors instead of single value, i.e. the column is a list instead of vector:

dt1 <- data.table(
  colA=   c('A1','A2','A3'), 
  colB=list('B1',c('B2a','B2b'),'B3'),
  colC=   c('C1','C2','C3'), 
  colD=   c('D1','D2','D3')
)

dt1
#   colA    colB colC colD
#1:   A1      B1   C1   D1
#2:   A2 B2a,B2b   C2   D2
#3:   A3      B3   C3   D3 

I need to reshape it to a long format unlisting that column colB. So far I do it like this:

dt1[,.(colB=unlist(colB)),by=.(colA,colC,colD)]
#   colA colC colD colB
#1:   A1   C1   D1   B1
#2:   A2   C2   D2  B2a
#3:   A2   C2   D2  B2b
#4:   A3   C3   D3   B3

it does the job but I don't like that I have to indicate all other column names explicitly in by=. Is there better way to do this?
(I'm sure it's already answered elsewhere but I couldn't find it so far)

P.S. ideally I would like to manage without any external packages

解决方案

Promoting my comment to an answer. Using:

dt1[,.(colB = unlist(colB)), by = setdiff(names(dt1), 'colB')]

gives:

   colA colC colD colB
1:   A1   C1   D1   B1
2:   A2   C2   D2  B2a
3:   A2   C2   D2  B2b
4:   A3   C3   D3   B3

Or as an alternative (a slight variation of @Frank's proposal):

dt1[rep(dt1[,.I], lengths(colB))][, colB := unlist(dt1$colB)][]

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