Accessing by variable column name in data.table - Error: `cannot change value of locked binding for '.SD'`

Question

This is related to my earlier question on convenience of data.table for loops and functions: How to use data.table within functions and loops? and related post: Data.table meta-programming.
This little code shows how conveniently this is done with data.table it is (e.g. compare to dplyr).

At first, I got cannot change value of locked binding for '.SD' error when I use get(strY) or .SD / .SDcols=colY below. But when I restarted the R Session, it all worked.

dt <- data.table(ggplot2::diamonds)
nY <- 1;                       nX <- c(5:7)
strY <- names(dt)[nY];         strX <- names(dt)[nX];        

dt[,strY, with=F] # OK
dt[,nY, with=F] # OK

dt[,get(strY)] # OK NOW: 
#NO MORE: Error in assign(ii, SDenv$.SDall[[ii]], SDenv) : 
#   cannot change value of locked binding for '.SD'
dt[, .SD, .SDcols=strX] # OK NOW: 
#NO MORE Error in assign(ii, SDenv$.SDall[[ii]], SDenv) : 
#   cannot change value of locked binding for '.SD'

I don't see the error you are "get"-ting. My console fills up with 53K values. Uggh. — IRTFM
– IRTFM, Commented Mar 3, 2017 at 22:29
Add library() statements. There is no diamonds data set available in my r session. — Frank
– Frank, Commented Mar 3, 2017 at 22:33
Anyway, dt[, ..strY] works fine for me, as does all of the code that is giving you errors. — Frank
– Frank, Commented Mar 3, 2017 at 22:35
You can find the link to delete your question below it. Otherwise, I guess you could post an answer further down, but I don't think this'll be of much benefit to future visitors. — Frank
– Frank, Commented Mar 6, 2017 at 15:44
I think this question is useful. Knowing that this error is solved by restarting the session clearly helped me. Maybe rephrase in a simpler way. — Picarus
– Picarus, Commented May 27, 2017 at 9:10

IVIM · Accepted Answer · 2017-03-08 04:03:10Z

5

This problem was resolved somehow by restarting the R session. - All lines work. This code has become the key work-stone for all my loop/function needs. Thanks to reviewers!

answered Mar 8, 2017 at 4:03

IVIM

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