[R] specifying dataframe column names in loops

Simon Goodman Simon.Goodman at ioz.ac.uk
Fri Jul 4 20:34:06 CEST 2003


Dear list members,

This is probably a naive question (from a new user), but I'm having problems
getting column 
names to be recognised in loop that is supposed to apply a set of
calculations in turn
to each column of a dataframe.

The dataframe has 33 columns of output from a simulation.
The columns each have a text name and I want to apply the same set of
calculations
to each column in turn. These include some self-defined functions that refer
back to the 
column in the current iteration.

Setting up a 'for' loop and using age[s] (where 'age' is the dataframe and
's' is the iterator) to specify
 each column works for things like 'max' and 'min'. However for functions
like 'density' or locfit, 
error messages are generated:

lf<-locfit(~age[s])
Error in model.frame(formula, rownames, variables, varnames, extras,
extranames,  : 
        invalid variable type

Similary if I try to use the 'names' function.

lf<-locfit(~names(age[s]))
Error in model.frame(formula, rownames, variables, varnames, extras,
extranames,  : 
        invalid variable type

So the question is how do I get functions like density or locfit to 
work in the loop in the same they would for specifying the name
of the column directly e.g. d<-density(ACER), where ACER is the name of the 
first column. 

Many thanks, Simon Goodman....


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