r function/loop to add column and value to multiple dataframes

Question

I have 8 data frames that I want to add a column called \'park\', then fill this column in w/ a value that comes from the last four characters of the data

Answer 1

A variation using Map and some "[<-" trickery:

vars <- ls(pattern="water_.")
l <- mget(vars)
names(l) <- substr(vars,nchar(vars)-3,nchar(vars))
do.call(rbind,Map("[<-",l,TRUE,"park",names(l)))