问题
When trying to store a vector in a data.table, this works only when the data.table has length of more than one.
Please find below a simplified version of the problem
library(data.table)
Working fine
dt <- data.table( a = c("a", "b"), l = list())
dt$l[[1]] <- c(1:3)
Results in:
a l
1: a 1,2,3
2: b
Producing Error
dt <- data.table( a = c("a"), l = list())
dt$l[[1]] <- c(1:3)
Error in [<-.data.table(x, j = name, value = value) : Supplied 3 items to be assigned to 1 items of column 'l'. The RHS length must either be 1 (single values are ok) or match the LHS length exactly. If you wish to 'recycle' the RHS please use rep() explicitly to make this intent clear to readers of your code.
Expected result in:
a l
1: a 1,2,3
回答1:
Is this what you're looking for?
dt <- data.table(a = "a", l = list())
dt[1L, l := list(list((1:3)))]
Results in:
a l
1: a 1,2,3
来源：https://stackoverflow.com/questions/57290514/error-when-trying-to-store-list-in-data-table-of-length-1