[R] evaluating NAs in a dataframe

[Peter Ehlers]

On 2010-12-08 12:10, Wade Wall wrote:
> Hi all,
>
> How can one evaluate NAs in a numeric dataframe column?  For example, I have
> a dataframe (demo) with a column of numbers and several NAs. If I write
> demo.df>= 10, numerals will return TRUE or FALSE, but if the value is
> "NA", "NA" is returned.  But if I write demo.df == "NA", it returns as "NA"
> also.  I know that I can remove NAs, but would like to keep the dataframe as
> is without creating a subset.  I basically want to add a line that evaluates
> the NA in the demo dataframe.
>
> As an example, I want to assign rows to classes based on values in
> demo$Area. Some of the values in demo$Area are "NA"
>
> for (i in 1:nrow(demo)) {
>    if (demo$Area[i]>  0&&  demo$Area[i]<  10) {Class[i]<-"S01"} ## 1-10 cm2
>    if (demo$Area[i]>= 10&&  demo$Area[i]<  25) {Class[i]<- "S02"} ##
> 10-25cm2
>    if (demo$Area[i]>= 25&&  demo$Area[i]<  50) {Class[i]<-"S03"} ## 25-50
> cm2
>    if (demo$Area[i]>= 50&&  demo$Area[i]<  100) {Class[i]<-"S04"} ## 50-100
> cm2
>    if (demo$Area[i]>= 100&&  demo$Area[i]<  200) {Class[i]<- "S05"} ##
> 100-200 cm2
>    if (demo$Area[i]>= 200&&  demo$Area[i]<  400) {Class[i]<- "S06"} ##
> 200-400 cm2
>    if (demo$Area[i]>= 400&&  demo$Area[i]<  800) {Class[i]<- "S07"} ##
> 400-800 cm2
>    if (demo$Area[i]>= 800&&  demo$Area[i]<  1600) {Class[i]<- "S08"} ##
> 800-1600 cm2
>    if (demo$Area[i]>= 1600&&  demo$Area[i]<  3200) {Class[i]<- "S09"} ##
> 1600-3200 cm2
>    if (demo$Area[i]>=3200) {Class[i]<- "S10"} ##>3200 cm2
>    }
>
> What happens is that I get the message "Error in if (demo$Area[i]>  0&&
> demo$Area[i]<  10) { : missing value where TRUE/FALSE needed"
>
You don't say what you want to have occur when x is NA. (I don't know
what 'evaluate NA' means.)

But why not just use something like:

  for(....){
    if(!is.na(x[i]){
      .... your stuff, preferably replacing '&&' with '&' ....
    } else {....}
  }

Peter Ehlers

> Thanks for any help
>
> Wade
>