R 数据表。需要使用分组和复杂条件过滤修改列

Question

这是数据样本：

zz <- "
id  Sub_Segment1    Sub_Segment2    Sub_Segment3    Sub_Segment4    Sub_Segment5
1   x   x1  r   y1  z1
1   x   x1  r   y1  z1
1   x   x1  r   y1  z1
1   x   x1  r   y1  z1
1   x   x1  r   y1  z1
1   x   x1  r   y1  z1
1   x   x1  r   y1  z1
2   y   x2  r   y2  z1
2   y   x2  r   y2  z1
2   y   x2  r   y2  z1
2   y   x2  r   y2  z1
2   y   x2  r   y2  z1
"

Data <- read.table(text=zz, header = TRUE)
setDT(Data)

如果我将修改应用到整个表，它会返回 NA：

Data[(length(unique(Sub_Segment1[Sub_Segment1!=""]))==1),name:="test" , by=id ]

返回：

 id Sub_Segment1 Sub_Segment2 Sub_Segment3 Sub_Segment4 Sub_Segment5 name
 1:  1            x           x1            r           y1           z1   NA
 2:  1            x           x1            r           y1           z1   NA
 3:  1            x           x1            r           y1           z1   NA
 4:  1            x           x1            r           y1           z1   NA
 5:  1            x           x1            r           y1           z1   NA
 6:  1            x           x1            r           y1           z1   NA
 7:  1            x           x1            r           y1           z1   NA
 8:  2            y           x2            r           y2           z1   NA
 9:  2            y           x2            r           y2           z1   NA
10:  2            y           x2            r           y2           z1   NA
11:  2            y           x2            r           y2           z1   NA
12:  2            y           x2            r           y2           z1   NA

但如果我在子段中只取一个具有恒定值的样本，它会起作用：

new_data = Data[id ==1]
new_data[(length(unique(Sub_Segment1[Sub_Segment1!=""]))==1),name:="test" , by=id ]

返回正确

   id Sub_Segment1 Sub_Segment2 Sub_Segment3 Sub_Segment4 Sub_Segment5 name
1:  1            x           x1            r           y1           z1 test
2:  1            x           x1            r           y1           z1 test
3:  1            x           x1            r           y1           z1 test
4:  1            x           x1            r           y1           z1 test
5:  1            x           x1            r           y1           z1 test
6:  1            x           x1            r           y1           z1 test
7:  1            x           x1            r           y1           z1 test

和

Data[id ==1,(length(unique(Sub_Segment1[Sub_Segment1!=""]))==1) ] # returns TRUE

我应该如何修改代码以将我的函数应用于 data.table 中的每一组数据集？

Answer 1

您可以将要编辑的行的标识移动到命令的一部分，您可以在其中选择列：

# load data table package
library(data.table)
# create the data table from string
Data <- read.table(text=zz, header = TRUE)
setDT(Data)
# group by and adjust where condition is matched
Data[, name := ifelse(length(unique(Sub_Segment1[Sub_Segment1!=""])) == 1, "test", NA) , by=id ]

除了 ifelse，您还可以在任何地方进行修改，然后进行过滤，或者使用连接操作。