R help - May 2005 - Q: changing the class of an object

Dear All,

I have a list of dataframes, each cell in every
dataframe (after I have cleaned up the dataframes) is
either real or NA  but have class character (I think).
I would like to know how to change the class of every
cell without using a for-loop. I currently have this

dataframes <- sapply(1: no.of.subs, function(k)
apply(dataframes[[k]], 2, function(x) {         
if(class(x)=="character") x <- as(x, "numeric"); x }))

but this neither changes the cells to numeric nor
keeps the dataframes in a list.

It creates one dataframe with number of rows=(no of
rows in a dataframe*no of colums) and number of
columns = no.of.subs

Can someone please help? Thanks in advance for any
help.

Dave

Datadrames don't have "cells" -- class, type, etc. is determined
on a column
by column basis (which is the same as a component by component basis, since
datframes are also lists) Please read "An Introduction to R" before
proceeding and posting so that you understand R's basic data structures and
conventions.

BTW -- what do you have against for loops? One should vectorize calculations
whenever possible,of course, but for loops are often useful and essentially
instantaneous. 

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Dave Evens
> Sent: Thursday, May 26, 2005 9:31 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Q: changing the class of an object
> 
> 
> Dear All,
> 
> I have a list of dataframes, each cell in every
> dataframe (after I have cleaned up the dataframes) is
> either real or NA  but have class character (I think).
> I would like to know how to change the class of every
> cell without using a for-loop. I currently have this
> 
> dataframes <- sapply(1: no.of.subs, function(k)
> apply(dataframes[[k]], 2, function(x) {         
> if(class(x)=="character") x <- as(x, "numeric"); x
}))
> 
> but this neither changes the cells to numeric nor
> keeps the dataframes in a list.
> 
> It creates one dataframe with number of rows=(no of
> rows in a dataframe*no of colums) and number of
> columns = no.of.subs
> 
> Can someone please help? Thanks in advance for any
> help.
> 
> Dave
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>

Dave Evens wrote:
> Dear All,
> 
> I have a list of dataframes, each cell in every
what is a cell?
> dataframe (after I have cleaned up the dataframes) is
> either real or NA  but have class character (I think).
> I would like to know how to change the class of every
> cell without using a for-loop. I currently have this
> 
> dataframes <- sapply(1: no.of.subs, function(k)
> apply(dataframes[[k]], 2, function(x) {         
> if(class(x)=="character") x <- as(x, "numeric"); x
}))
> 
> but this neither changes the cells to numeric nor
> keeps the dataframes in a list.
> 
> It creates one dataframe with number of rows=(no of
> rows in a dataframe*no of colums) and number of
> columns = no.of.subs
> 
> Can someone please help? Thanks in advance for any
> help.

A simple way is

   data.frame(sapply(X, as.numeric))

but I guess the real problem is some steps before. You should take a 
look why you got character vectors in your data.frame rather than 
numeric ones.

Uwe Ligges


> Dave
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html