R help - May 2012 - for loop, error in model frame.default ... variable lengths differ

I'm failing to get a for loop working.  I'm sure it's something
simple, and I
have found some posts relating to it, but I'm just not understanding why
this isn't working. 

I have a data frame and would like to loop through specific column names,
using aggregate() within a for loop.  There are NA's scattered throughout
the data frame and I'm thinking it has something to do with that, but I
haven't been able to fix it.

vars <- colnames(df)[c(10,12,16,18,20,21,24:29,45)]
 for(i in 1:length(vars)) {
    aggregate(colnames(df)[i] ~ x1 + x2 + x3, df, mean,
na.action=na.exclude)
    }

I get this error: 
Error in model.frame.default(formula = colnames(df)[i] ~ x1 + x2 +   : 
  variable lengths differ (found for 'x1')

There are probably much better ways to do this, and I would be happy to get
suggestions, but mostly I would like to know why the code isn't working.

Thanks-
Peter

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No data, not reproducible.

I think you should be using na.omit, though.
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Peter Keller <kellerp.l at gmail.com> wrote:
>I'm failing to get a for loop working.  I'm sure it's something
simple,
>and I
>have found some posts relating to it, but I'm just not understanding
>why
>this isn't working. 
>
>I have a data frame and would like to loop through specific column
>names,
>using aggregate() within a for loop.  There are NA's scattered
>throughout
>the data frame and I'm thinking it has something to do with that, but I
>haven't been able to fix it.
>
>vars <- colnames(df)[c(10,12,16,18,20,21,24:29,45)]
> for(i in 1:length(vars)) {
>    aggregate(colnames(df)[i] ~ x1 + x2 + x3, df, mean,
>na.action=na.exclude)
>    }
>
>I get this error: 
>Error in model.frame.default(formula = colnames(df)[i] ~ x1 + x2 +   : 
>  variable lengths differ (found for 'x1')
>
>There are probably much better ways to do this, and I would be happy to
>get
>suggestions, but mostly I would like to know why the code isn't
>working.
>
>Thanks-
>Peter
>
>--
>View this message in context:
>http://r.789695.n4.nabble.com/for-loop-error-in-model-frame-default-variable-lengths-differ-tp4630698.html
>Sent from the R help mailing list archive at Nabble.com.
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

Hi

You did not provide data but I can see some problems in your code. See 
inline.
> 
> I'm failing to get a for loop working.  I'm sure it's something
simple,
and I
> have found some posts relating to it, but I'm just not understanding
why
> this isn't working. 
> 
> I have a data frame and would like to loop through specific column 
names,
> using aggregate() within a for loop.  There are NA's scattered 
throughout
> the data frame and I'm thinking it has something to do with that, but I
> haven't been able to fix it.
> 
> vars <- colnames(df)[c(10,12,16,18,20,21,24:29,45)]
>  for(i in 1:length(vars)) {
So i is actually values from 1 to length of vars variable.
>     aggregate(colnames(df)[i] ~ x1 + x2 + x3, df, mean,
and you select variables from df[,1] to df[, length(vars)], which is 
probably not what you want.
What is x1-x3? are they variables in df?
> na.action=na.exclude)
for mean the correct statement is na.rm=TRUE
>     }
> 
> I get this error: 
> Error in model.frame.default(formula = colnames(df)[i] ~ x1 + x2 +   : 
>   variable lengths differ (found for 'x1')
Maybe x1 has different length as df. What length(x1) and dim(df) tells 
you?

Regards
Petr
> 
> There are probably much better ways to do this, and I would be happy to 
get
> suggestions, but mostly I would like to know why the code isn't
working.
> 
> Thanks-
> Peter
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/for-loop-
> error-in-model-frame-default-variable-lengths-differ-tp4630698.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.