Question

我有以下设置，我想剪切文本字符串，生成一个列表，然后重新分配回data.table作为嵌套列。它适用于n> 1行，但如果n = 1行则不行。我该怎么做才能确保一致性：

library(data.table)

cutdash <- function(x) {strsplit(x, '-')}

## n > 1 row
x <- data.frame(
    text = c("I paid for books-He was not interesting in his teaching.", 'good'),
    id = 1:2, stringsAsFactors = FALSE)

## n = 1 row
y <- data.frame(text = "I paid for books-He was not interesting in his teaching.", 
    id = 3, stringsAsFactors = FALSE)


## good
x2 <- data.table::data.table(x)
x2[, text := cutdash(text)][]

##                                                        text id
## 1: I paid for books,He was not interesting in his teaching.  1
## 2:                                                     good  2

## bad 
y2 <- data.table::data.table(y)
y2[, text := cutdash(text)][]

##                text id
## 1: I paid for books  3

## Warning message:
## In `[.data.table`(y2, , `:=`(text, cutdash(text))) :
##   Supplied 2 items to be assigned to 1 items of column 'text' (1 unused)

不是第一个只有1行的数据帧只允许重新分配第一个元素。

Answer 1

您需要使用str_split或list将您的号召打包到.（作为data.table [内的列表别名。就像这样：

y2[, text := .(cutdash(text))][]

或

y2[, text := list(cutdash(text))][]

n = 1行与n的参考分配的data.table一致性＆gt; 1

1 个答案: