通过引用列名称在数据表中聚合 [英] Aggregation in data.table by reference to column names

问题描述

我想通过数据表中的列列来聚合一些列。但是，我想避免使用引号外的列名称（在 by =。（desiredColumn1，desiredColumn2），即）。我很高兴使用列名或列索引。例如：

I would like to aggregate some columns by a list of columns in a data.table. However, I would like to refrain from using the column names outside the quotation marks (in the by = .(desiredColumn1, desiredColumn2), that is). I am happy with using either the column names or the column indices. For example:

library(data.table)
x = as.data.table(iris)
x[, sum(Sepal.Width), by = .(Sepal.Length, Species)] # I want to avoid doing this
x[, sum("Sepal.Width"), by = .("Sepal.Length", "Species"), with = FALSE] # this does not work
x[, sum("Sepal.Width"), by = .(1, 5), with = FALSE]

有关如何执行此操作的任何想法吗？

Any ideas on how to do this?

推荐答案

我们可以使用 c 与名称

x[, sum(Sepal.Width), by = c(names(x)[c(1, 5)])] 

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