Is there a way to assign a value to a specific column within a data frame? e.g.,
dat2 = data.frame(c1 = 101:149, VAR1 = 151:200)
j = "dat2[,"VAR1"]" ## or, j = "dat2[,2]"
assign(j,1:50)
The approach above doesn't work. Neither does this:
j = "dat2"
assign(get(j)[,"VAR1"],1:50)
lets assume that we have a valid data.frame with 50 rows in each
dat2 <- data.frame(c1 = 1:50, VAR1 = 51:100)
1 . Don't use assign
and get
if you can avoid it.
"dat2[,"VAR1"]"
is not valid in R
.
You can also note this from the help page for assign
assign does not dispatch assignment methods, so it cannot be used to set elements of vectors, names, attributes, etc.
Note that assignment to an attached list or data frame changes the attached copy and not the original object: see attach and with.
A column of a data.frame is an element of a list
What you are looking for is [[<-
# assign the values from column (named element of the list) `VAR1`
j <- dat2[['VAR1']]
If you want to assign new values to VAR1
within dat2
,
dat2[['VAR1']] <- 1:50
To manipulate entirely using character strings using get
and assign
assign('dat2', `[[<-`(get('dat2'), 'VAR1', value = 2:51))
if you want to assign by reference within a data.frame
or data.table
(replacing an existing column only) then set
from the data.table
package works (even with data.frames
)
library(data.table)
set(dat2, j = 'VAR1', value = 5:54)
eval
and bquote
dat1 <- data.frame(x=1:5)
dat2 <- data.frame(x=2:6)
for(x in sapply(c('dat1','dat2'),as.name)) {
eval(bquote(.(x)[['VAR1']] <- 2:6))
}
eapply
Or if you use a separate environment
ee <- new.env()
ee$dat1 <- dat1
ee$dat2 <- dat2
# eapply returns a list, so use list2env to assign back to ee
list2env(eapply(ee, `[[<-`, 'y', value =1:5), envir = ee)