[R] easy loop question

[David Winsemius]

On Jan 12, 2011, at 10:54 PM, Sebastián Daza wrote:

> Hi everyone,
>
> I am new in R and programming. I have tried to remove the values out  
> of range in some variables using a loop:
>
> 1)
>
> var  <- names(est8vo[, 77:83])   # I got the variable names
>
> > var
> [1] "p16.1" "p16.2" "p16.3" "p16.4" "p16.5" "p16.6" "p16.7"
>
> for (i in 1:7)  {
> var.i  <- var[i]
> est8vo$var.i[ est8vo$var.i==3] <- 99

You CANNOT use names like that. (It makes no sense to supply a vector  
argument to "$".) If you want to change every instance of 3 within  a  
group of columns. See if this works

est8vo[, 77:83] <-  sapply( est8vo[, 77:83], function(x) ifelse(x==3,  
99, x) )


>  }
>
> I got this error:
>
> Error in `$<-.data.frame`(`*tmp*`, "var.i", value = numeric(0)) :
>  replacement has 0 rows, data has 215700
>
>
> 2) The second step would be to define the factors, but I got the  
> same error:

est8vo[, 77:83] <- sapply(est8vo[, 77:83] , factor, labels=c("vacío",  
"sí", "no", "doble marca"))

>
> for (i in 1:7)  {
> var.i  <- var[i]
> est8vo$var.i    <- factor(est8vo$var.i,

Wrong. Wrong. Wrong. And please forget about using "$" inside loops in  
the left-hand side. It is not designed for that.

>  levels=c(0, 1, 2, 99),
>  labels=c("vacío", "sí", "no", "doble marca")
>  )
>  }
>
>
> I don't know how to do it.
> Thank you in advance!
> Sebastian
>
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David Winsemius, MD
West Hartford, CT