[R] Using na.omit() on the output of na.omit()

[Shu Fai Cheung]

Hi All,

I noticed a behavior of na.omit() that I am not sure is intended.

This is adapted from the example of na.omit()

> DF <- data.frame(x = c(1, 2, 3), y = c(NA, 10, 1))
> DF_omitted <- na.omit(DF)
> attr(DF_omitted, "na.action")
1
1
attr(,"class")
[1] "omit"
> DF_omitted2 <- na.omit(DF_omitted)
> attr(DF_omitted2, "na.action")
1
1
attr(,"class")
[1] "omit"

In the first call to na.omit(), the output, DF_omitted, correctly has only
two rows, with Row 1 removed, and 'na.action' stores the removed row number.

In the second call of na.omit(), no cases are removed because DF_omitted
has no missing data. However, the attribute 'na.action' is retained,
indicating that Row 1 was removed.

To my understanding of na.omit(), this occurred because, in the second call
of na.omit(), no rows were omitted, and so the original object was
returned, along with the attribute 'na.action' from the first call.

>From the "perspective" of the second call, no rows were omitted.
Should 'na.action'
be NULL (i.e., not set), as in the following example?

> DF2 <- data.frame(x = c(1, 2, 3), y = c(3, 10, 1))
> DF2_omitted <- na.omit(DF2)
> attr(DF2_omitted, "na.action")
NULL

Or is this behavior of na.omit() intended?

Regards,
Shu Fai

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