data.table:将setkey与列名变量一起使用 [英] data.table: using setkey with a column name variable

问题描述

我有一个变量名保存到字符串变量 which_id 中.

I have a variable name saved into the string variable which_id.

W 是一个数据表.如何使用 which_id 在 W 上调用 setkey ?

W is a data.table. How do I call setkey on W with which_id ?

这是我尝试过的

 > eval( paste( 'setkey(W,' , which_id , ')' ) )
[1] "setkey(W, customer_id_A )"

但是对 tables()的调用显示 customer_id_A 键没有用.

But a call to tables() shows that the customer_id_A key didn't take.

 > evalq( paste( 'setkey(W,' , which_id , ')' ) )
[1] "setkey(W, customer_id_A )"

customer_id_A 密钥仍然没有用.

 > setkeyv( W , cols=which_id )

和

 > setkeyv( W , cols=c( which_id ) )

->一样， customer_id_A 键不存在.

有指针吗?

推荐答案

setkeyv 应该可以.这是一个可重现的示例:

setkeyv should work. Here is a reproducible example:

library(data.table)
W <- data.table(customer_id_A = 1:2)
which_id <- "customer_id_A"
setkeyv(W, which_id)
tables()
##      NAME NROW MB COLS          KEY          
## [1,] W       2 1  customer_id_A customer_id_A
## Total: 1MB

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