[R] To many NA's from mean(..., na.rm=T) when a column is all NA's

[Achim Zeileis]

On Mon, 13 Jun 2005 11:05:46 -0600 (MDT) Jim Robison-Cox wrote:

> Dear R-help folks,
> 
> I am seeing unexpected behaviour from the function mean
> with option na.rm =TRUE (which is removing a whole column of a data
> frame or matrix.
> 
> example:
> 
> testcase <- data.frame( x = 1:3, y = rep(NA,3))

In addition to what Sundar already wrote: In the code above x is numeric
and y logical, hence as.matrix() will not do what you want (create a
"character" matrix). Probably it is more appropriate to do

  testcase <- data.frame( x = 1:3, y = as.numeric(rep(NA,3)))

hth,
Z

> mean(testcase[,1], na.rm=TRUE)
> [1] 2
> mean(testcase[,2], na.rm = TRUE)
> [1] NaN
> 
>   OK, so far that seems sensible.  Now I'd like to compute both means
>   at
> once:
> 
>   lapply(testcase, mean, na.rm=T)   ## this works
> $x
> [1] 2
> 
> $y
> [1] NaN
> 
>   But I thought that this would also work:
> 
> apply(testcase, 2, mean, na.rm=T)
>  x  y
> NA NA
> Warning messages:
> 1: argument is not numeric or logical: returning NA in:
> mean.default(newX[, i], ...)
> 2: argument is not numeric or logical: returning NA in:
> mean.default(newX[, i], ...)
> 
>  Summary:
>   If I have a data frame or a matrix where one entire column is NA's,
> mean(x, na.rm=T) works on that column, returning NaN, but fails using
> apply, in that apply returns NA for ALL columns.
>   lapply works fine on the data frame.
> 
>   If you wonder why I'm building data frames with columns that could
>   be
> all missing -- they arise as output of a simulation.  The fact that
> the entire column is missing is informative in itself.
> 
> 
>   I do wonder if this is a bug.
> 
> Thanks,
> Jim
> 
> Jim Robison-Cox               ____________
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> 
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