for loop, error in model frame.default ... variable lengths differ

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?

aggregate(colnames(airquality)[1] ~ Month, airquality, mean, na.rm=T)

nm <- colnames(airquality)[1]
ff <- formula(bquote(.(as.name(nm))~Month))
aggregate(ff, airquality, mean, na.rm=T)

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

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