R-在不计算NA的情况下获取每组的值数 [英] R - Get number of values per group without counting NAs

问题描述

因此，我试图计算一列中每个组的值数量，而不计算NA. 我尝试使用长度"来执行此操作，但是在查看每个组的值时，我无法弄清楚如何告诉长度"保持NA.

So I'm trying to count the number of values per group in a column without counting the NAs. I've tried doing it with "length" but I can't figure out how to tell "length" to leave the NAs be, when in the context of looking at values per group.

我发现了类似的问题，但不知道如何将解决方案应用于我的案子:

I've found similar problems but couldn't figure out how to apply the solutions to my case:

在r中不包括NA的列的长度

http://r .789695.n4.nabble.com/Length-of-vector-without-NA-s-td2552208.html

我创建了一个最小的工作示例来说明问题:

I've created a minimal working example to illustrate the problem:

# making some data
value <- c(3,10,9,"NA",5,"NA","NA",4)
group <- c("A","A","B","C","B","A","A","C")

example <- data.frame(value, group)

example
#     value group
# 1     3     A
# 2    10     A
# 3     9     B
# 4    NA     C
# 5     5     B
# 6    NA     A
# 7    NA     A
# 8     4     C


# trying to extract the number of values (without counting NAs) for each group
n.example <- tapply(example$value, list(example$group), length)
n.example
# A B C 
# 4 2 2

#Correct answer would be:
# A B C 
# 2 2 1  

我将不胜感激！

Thx， 船长

推荐答案

如果我们使用不带引号的真实NA，则可以使用is.na和table来查找计数.

If we are using real NAs without quoting, we can use is.na and table to find the count.

table(!is.na(value), group)[2,]
#A B C 
#2 2 1 

数据

value <- c(3,10,9,NA,5,NA,NA,4)
group <- c("A","A","B","C","B","A","A","C")

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