1
我很好奇是否可以將[
或join
函數應用於data.tables列表。 我可以使用函數來處理列表中的每個元素,但是當使用lapply
將函數應用於整個列表時,我會收到一個錯誤。將數據表加入運算符應用於數據表列表
### Require data.table
require(data.table)
### Create master data.table
data <- data.table(id = letters[1:10], val = 1:10, key = 'id')
### Create data tables to be joined
a <- data.table(id = letters[1:10], height = rnorm(n = 10, mean = 150, sd = 10), key = 'id')
b <- data.table(id = letters[1:10], weight = rnorm(n = 10, mean = 140, sd = 20), key = 'id')
### Create a list of data tables to be joined
l <- list(a, b)
### Join data tables (Works)
`[`(l[[1]], data)
`[`(l[[2]], data)
### Apply join function to a list. Doesn't work. Why?
lapply(l, `[`, data)
Error in `[.default`(x, i) : invalid subscript type 'list'
此錯誤使我不知道當[
被用於R是如何能夠區分加入,與當它被用於提取從物體的元素。例如:
### Extract first column from each data.table in 'l'
lapply(l, `[`, 1)