在R中缩放data.table列的子集

Question

我想scale在我的一部分列中data.table.我希望有很多这样的,scale所以我想避免通过名称来指定它们.没有缩放的列,我只想按原样返回.这是我希望可以工作,但它没有:

require(data.table)
x = data.table(id=1:10, a=sample(1:10,10), b=sample(1:10,10), c=sample(1:10,10))
> dput(x)
structure(list(id = 1:10, a = c(1L, 6L, 10L, 7L, 5L, 3L, 2L, 
4L, 9L, 8L), b = c(4L, 9L, 5L, 7L, 6L, 1L, 8L, 10L, 3L, 2L), 
    c = c(2L, 7L, 5L, 6L, 4L, 1L, 10L, 9L, 8L, 3L)), .Names = c("id", 
"a", "b", "c"), row.names = c(NA, -10L), class = c("data.table", 
"data.frame"), .internal.selfref = <pointer: 0x1a85d088>)

sx = x[,c(id, lapply(.SD, function(v) as.vector(scale(v)))), .SDcols = colnames(x)[2:4]]
   Error in eval(expr, envir, enclos) : object 'id' not found

有什么建议？

Answer 1

您还可以通过引用分配数据表的副本

sc <- names(x)[2:4]

sx <- copy(x)[ , (sc) := as.data.table(scale(.SD)), .SDcols = sc]

scale返回一个矩阵,而iirc data.table不喜欢矩阵列.

要么,

sx <- copy(x)[ , (sc) := lapply(.SD,scale), .SDcols = sc]

[在括号(sc)告诉data.table采取自变量的值的LHS值在呼叫范围,而不是列名sc本身.]