# [R] Adding two or more columns of a data frame for each row when NAs are present.

Dennis Murphy djmuser at gmail.com
Mon Nov 21 05:30:51 CET 2011

```Hi:

Does this work for you?

> yy
Q20 Q21 Q22 Q23 Q24
1   0   1   2   3   4
2   1  NA   2   3   4
3   2   1   2   3   4

rowSums(yy, na.rm = TRUE)
1  2  3
10 10 12

# Use a subset of the variables in yy:
selectVars <- paste('Q', c(20, 21, 24), sep = '')
rowSums(yy[, selectVars], na.rm = TRUE)
1 2 3
5 5 7

HTH,
Dennis
On Sun, Nov 20, 2011 at 12:38 PM, Ian Strang <hamamelis at ntlworld.com> wrote:
>
> I am fairly new to R and would like help with the problem below. I am trying
> to sum and count several rows in the data frame yy below. All works well as
> in example 1. When I try to add the columns, with an NA in Q21, I get as NA
> as mySum. I would like NA to be treated as O, or igored.
> I wrote a function to try to count an NA element as 0, Example 3 function.
> It works with a few warnings, Example 4, but still gives NA instead of the
> addition when there is an NA in an element.
>
> In Example 6 & 7, I tried using sum() but it just sums the whole data frame,
> I think,
>
> How do I add together several columns giving the result for each row in
> mySum? NA should be treated as a 0. Please, note, I do not want to sum all
> the columns, as I think rowSums would do, just the selected ones.
>
> Ian,
>
>> yy <- read.table( header = T, sep=",", text =     ## to create a data
>> frame
> + "Q20, Q21, Q22, Q23, Q24
> +  0,1, 2,3,4
> +  1,NA,2,3,4
> +  2,1, 2,3,4")
> +  yy
>  Q20 Q21 Q22 Q23 Q24
> 1   0   1    2   3   4
> 2   1  NA   2   3   4
> 3   2   1    2   3   4
>
>> x <- transform( yy,     ############## Example 1
> +   mySum = as.numeric(Q20) + as.numeric(Q22) + as.numeric(Q24),
> +   myCount =
> as.numeric(!is.na(Q20))+as.numeric(!is.na(Q21))+as.numeric(!is.na(Q24))
> + )
> + x
>  Q20 Q21 Q22 Q23 Q24 mySum myCount
> 1   0   1    2   3   4     6       3
> 2   1  NA   2   3   4     7       2
> 3   2   1    2   3   4     8       3
>>
> + x <- transform( yy,     ################ Example 2
> +   mySum = as.numeric(Q20) + as.numeric(Q21) + as.numeric(Q24),
> +   myCount =
> as.numeric(!is.na(Q20))+as.numeric(!is.na(Q21))+as.numeric(!is.na(Q24))
> + )
> + x
>  Q20 Q21 Q22 Q23 Q24 mySum myCount
> 1   0   1    2   3   4     5       3
> 2   1  NA   2   3   4    NA       2
> 3   2   1    2   3   4     7       3
>
>> NifAvail <- function(x) { if (is.na(x)) x<-0 else x <- x   ###############
>> Example 3
> +   return(as.numeric(x))
> + } #end function
> + NifAvail(5)
> [1] 5
> + NifAvail(NA)
> [1] 0
>
>> x <- transform( yy,
> +   mySum = NifAvail(Q20) + NifAvail(Q22) + NifAvail(Q24),
>  ############### Example 4
> +   myCount =
> as.numeric(!is.na(Q20))+as.numeric(!is.na(Q21))+as.numeric(!is.na(Q24))
> + )
> Warning messages:
> 1: In if (is.na(x)) x <- 0 else x <- x :
>  the condition has length > 1 and only the first element will be used
> 2: In if (is.na(x)) x <- 0 else x <- x :
>  the condition has length > 1 and only the first element will be used
> 3: In if (is.na(x)) x <- 0 else x <- x :
>  the condition has length > 1 and only the first element will be used
>> x
>  Q20 Q21 Q22 Q23 Q24 mySum myCount
> 1   0   1    2   3   4     6       3
> 2   1  NA   2   3   4     7       2
> 3   2   1    2   3   4     8       3
>> x <- transform( yy,
> +   mySum = NifAvail(Q20) + NifAvail(Q21) + NifAvail(Q24),
> ################ Example 5
> +   myCount =
> as.numeric(!is.na(Q20))+as.numeric(!is.na(Q21))+as.numeric(!is.na(Q24))
> + )
> Warning messages:
> 1: In if (is.na(x)) x <- 0 else x <- x :
>  the condition has length > 1 and only the first element will be used
> 2: In if (is.na(x)) x <- 0 else x <- x :
>  the condition has length > 1 and only the first element will be used
> 3: In if (is.na(x)) x <- 0 else x <- x :
>  the condition has length > 1 and only the first element will be used
>> x
>  Q20 Q21 Q22 Q23 Q24 mySum myCount
> 1   0   1    2   3   4     5       3
> 2   1  NA   2   3   4    NA       2
> 3   2   1    2   3   4     7       3
>
>
>> x <- transform( yy,                                        ############
>> Example 6
> +   mySum = sum(as.numeric(Q20), as.numeric(Q21), as.numeric(Q23), na.rm=T),
> +   myCount =
> as.numeric(!is.na(Q20))+as.numeric(!is.na(Q21))+as.numeric(!is.na(Q24))
> + )
> + x
>  Q20 Q21 Q22 Q23 Q24 mySum myCount
> 1   0   1    2   3   4    14       3
> 2   1  NA   2   3   4    14       2
> 3   2   1    2   3   4    14       3
>
>> x <- transform( yy,                                       #############
>> Example 7
> +   mySum = sum(as.numeric(Q20), as.numeric(Q22), as.numeric(Q23), na.rm=T),
> +   myCount =
> as.numeric(!is.na(Q20))+as.numeric(!is.na(Q21))+as.numeric(!is.na(Q24))
> + )
> + x
>  Q20 Q21 Q22 Q23 Q24 mySum myCount
> 1   0   1    2   3   4    18       3
> 2   1  NA   2   3   4    18       2
> 3   2   1    2   3   4    18       3
>
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