[R] conditional coding question

[David Winsemius]

On Nov 7, 2012, at 3:07 PM, haps wrote:

> I have a big dataset. I want to create a new factor variable with certain
> conditions based on two existing numeric variables. 
> Existing variables: indinc (range: 0 to 16), groupinc (range -3 to 5)
> Conditional values that 'incorp' will take:
> If groupinc = 5, then ‘cons’;
> If groupinc is -3 : -2, AND indinc <  9, then  ‘ethnat’;
> If groupinc is -2 : -1, AND indinc > 8, then ‘civic’;
> If groupinc is 1 : 4, AND indinc > 8, then ‘libmul’;
> The rest of the values should be coded as NA.
> #here is my code after attaching the data (4408 is the number of
> observations):#
> incorp <-

You are making an inappropriate double assignment. This assignment will shoot off your foot.  I believe that for loops return NULL, so even if your loop succeeded in making all the assignments inside the body which it did not and I believe could not even with syntactic surgery for the reason expanded on below, the incorp value would be NULL afterward.

> incorp= 1:10; incorp <- for (i in seq_along(incorp) ) { incorp[i] = 2*incorp[i] }
> incorp
NULL



>  for (i in 1:4408) {
>    if (groupinc[i] == 5) {
>      incorp[i] = 'cons'
>    } else if ((groupinc[i] == -3:-2) & (indinc[i] < 9)) {

I doubt very much that you should be testing for (groupinc[i] == -3:-2)

I suspect you what to be testing whether groupinc[i] is in the range -3 to -2

For that you have a couple of choices. If you know for a fact that groupinc[i] will be integer valued (and is not really a double/float value then you could do:

if ( groupinc[i[ %in% -3:-2 )

If group inc[i] is a floating point number you should test:

if( groupinc[i] >= -3 & groupinc[i] <= -2)


>      incorp[i] = 'ethnat'
>    } else if ((groupinc[i] == 1:4) & (indinc[i] > 8)) {
>      incorp[i] = 'libmul'
>    } else if ((groupinc[i] == -2:-1) & (indinc[i] > 8)) {
>      incorp[i] = 'civic' 
>    } else = NA
>  }
> #error message#
> Error: unexpected '=' in:
> "      incorp[i] = 'civic' 
>    } else ="

That is a syntactic error, but I suspect you have semantic errors as mentioned above.

> 
> 
> 
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David Winsemius, MD
Alameda, CA, USA