按NA在R中汇总 [英] Aggregate by NA in R

问题描述

有人知道如何通过R中的NA进行聚合.

Does anybody know how to aggregate by NA in R.

如果您使用以下示例

a <- matrix(1,5,2)
a[1:2,2] <- NA
a[3:5,2] <- 2
aggregate(a[,1], by=list(a[,2]), sum)

输出为:

Group.1 x
2       3

但是有一种方法可以使输出像这样在输出中包含NA:

But is there a way to get the output to include NAs in the output like this:

Group.1 x
2       3
NA      2

谢谢

推荐答案

您可能要考虑使用rowsum()，而不是aggregate().实际上，它是为在矩阵上进行此精确运算而设计的，并且已知比aggregate()快得多.我们可以使用addNA()将NA添加到a[, 2]的因子水平.这样可以确保NA显示为分组变量.

Instead of aggregate(), you may want to consider rowsum(). It is actually designed for this exact operation on matrices and is known to be much faster than aggregate(). We can add NA to the factor levels of a[, 2] with addNA(). This will assure that NA shows up as a grouping variable.

rowsum(a[, 1], addNA(a[, 2]))
#      [,1]
# 2       3
# <NA>    2

如果您仍然想使用aggregate()，也可以合并addNA().

If you still want to use aggregate(), you can incorporate addNA() as well.

aggregate(a[, 1], list(Group = addNA(a[, 2])), sum)
#   Group x
# 1     2 3
# 2  <NA> 2

还有 data.table -

library(data.table)
as.data.table(a)[, .(x = sum(V1)), by = .(Group = V2)]
#    Group x
# 1:    NA 2
# 2:     2 3

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