聚合时将列名称动态添加到data.table

问题描述

我知道在通过引用创建列时（使用：= ），我们可以动态添加列名，例如此处：。

I know we can dynamically add column names when creating columns by reference (using :=), as described e.g. here: Dynamic column names in data.table.

但是，我希望在聚合时动态添加列名。您可以帮忙吗？

However, I'm looking to dynamically add column names when we aggregate. Can you help with this?

test_dtb <- data.table(a = sample(1:100, 100), b = sample(1:100, 100), id = rep(1:10, 10))
m = "blah"
test_dtb[ , list((m) = mean(b)), by = id]

我得到的错误是

Error: unexpected '=' in "test_dtb[ , list((m) =

推荐答案

如lukeA的注释中所述，可以使用 setNames ：

As mentioned in the comments by lukeA, setNames can be used:

m <- c("blah", "foo")
test_dtb[ , setNames(list(mean(b), median(b)), m), by = id]

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