如何避免dcast()输出中的NA列? [英] How to avoid NA columns in dcast() output?

问题描述

我如何避免 从reshape2软件包输出的dcast()列?

How can I avoid NA columns in dcast() output from the reshape2 package?

在此虚拟示例中，dcast()输出将包含NA列:

In this dummy example the dcast() output will include an NA column:

require(reshape2)
data(iris)
iris[ , "Species2"] <- iris[ , "Species"]
iris[ 2:7, "Species2"] <- NA
(x <- dcast(iris, Species ~ Species2, value.var = "Sepal.Width", 
            fun.aggregate = length))
##     Species setosa versicolor virginica NA
##1     setosa     44          0         0  6
##2 versicolor      0         50         0  0
##3  virginica      0          0        50  0

对于有些类似的用例，table()确实有一个选项可以避免这种情况:

For a somewhat similar usecase, table() does have an option that allows to avoid this:

table(iris[ , c(5,6)], useNA = "ifany")  ##same output as from dcast()
##            Species2
##Species      setosa versicolor virginica <NA>
##  setosa         44          0         0    6
##  versicolor      0         50         0    0
##  virginica       0          0        50    0
table(iris[ , c(5,6)], useNA = "no")  ##avoid NA columns
##            Species2
##Species      setosa versicolor virginica
##  setosa         44          0         0
##  versicolor      0         50         0
##  virginica       0          0        50

dcast()是否具有类似的选项，可以删除输出中的NA列?如何避免出现NA列? (此功能有许多相当隐秘的选项，已严格记录在案，我无法完全理解...)

Does dcast() have a similar option that removes NA columns in the output? How can I avoid getting NA columns? (This function has a number of rather cryptic options that are sternly documented and that I cannot quite grasp...)

推荐答案

这是我如何解决它的方法:

Here is how I was able to get around it:

iris[is.na(iris)] <- 'None'

x <- dcast(iris, Species ~ Species2, value.var="Sepal.Width", fun.aggregate = length)

x$None <- NULL

这个想法是用"None"替换所有NA，以便dcast创建一个名为"None"而不是"NA"的列.然后，如果不需要，您可以在下一步中将该列删除.

The idea is that you replace all the NAs with 'None', so that dcast creates a column called 'None' rather than 'NA'. Then, you can just delete that column in the next step if you don't need it.

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