[R] selecting columns based on partial names

[Jim Lemon]

On Thu, 19 Jun 2014 02:50:20 PM Chris Dolanc wrote:
> Hello,
> 
> I have a data frame with > 5000 columns and I'd like to be able to 
make
> subsets of that data frame made up of certain columns by using 
part of
> the column names. I've had a surprisingly hard time finding 
something
> that works by searching online.
> 
> For example, lets say I have a data frame (df) of 2 obs. of 6 
variables.
> The 6 variables are called "1940_tmax", "1940_ppt", "1940_tmin",
> "1941_tmax", "1941_ppt", "1941_tmin". I want to create a new data 
frame
> with only the variables that have "ppt" in the variable (column) 
name,
> so that it looks like this:
> 
> plot name    1940_ppt    1941_ppt
> 774-CL                    231               344
> 778-RW                  228               313
> 
Hi Chris,
One way is to get the column indices:

grep("ppt",names(df))
[1] 2 5

so,

newdf<-df[grep("ppt",names(df))]

and then you apparently want to add a column with some other 
information, so probably:

newdf<-cbind(<something_else>,
 df[grep("ppt",names(df))])

Jim