# [R] using pmax in presence of NAs

peter dalgaard pdalgd at gmail.com
Wed Nov 16 22:21:34 CET 2016

```> On 16 Nov 2016, at 21:58 , Dimitri Liakhovitski <dimitri.liakhovitski at gmail.com> wrote:
>
> Hello!
>
> I need to calculate the maximum of each row of a data frame.
> This works:
>
>  x <- data.frame(a = 1:5, b=11:15, c=111:115)
>  x
>  do.call(pmax, x)
>  111 112 113 114 115
>
> However, how should I modify it if my data frame has NAs?
> I'd like it to ignore NAs and return the maximum of all non-NAs in each row:
>
>  x <- data.frame(a = c(1:5), b=11:15, c=c(111:114,NA))
>  x
> I'd like it to return:
>  111 112 113 114 15
>
> Thanks a lot!

The first thing to notice is that pmax allows na.rm=TRUE, so it works fine to do

> pmax(a = c(1:5), b=11:15, c=c(111:114,NA), na.rm=TRUE)
 111 112 113 114  15

I.e., it is your desire to use do.call() that is the challenge. The 2nd argument should be a list containing the arguments as in the above call, so this works too

> do.call(pmax, list(a = c(1:5), b=11:15, c=c(111:114,NA), na.rm=TRUE))
 111 112 113 114  15

The form do.call(pmax,x) uses the fact that a data.frame is a kind of list. What you need to do is to tack on the element na.rm=TRUE. This works

> do.call(pmax, c(x, list(na.rm=TRUE)))
 111 112 113 114  15

and it even works without the list()

> do.call(pmax, c(x, na.rm=TRUE))
 111 112 113 114  15

-pd

>
> --
> Dimitri Liakhovitski
>
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--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

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