r - Accessing a non existent column of a data.table with dollar sign -


i using (probably outdated) version 1.10.4 of data.table r version 3.3.2 (2016-10-31). can access non-existent columns dollar sign. behaviour wanted?

code:

realoffloads = data.table(bag_tag = c(1,2,3)) realoffloads = realoffloads[, .(bag_tag, offload_real = t)] "offload" %in% names(realoffloads) x = realoffloads$offload

although getting 'false' answer question whether or not column 'offload' exists getting out of (t,t,t) when accessing using dollar sign.

i using pretty in code little scared :-()

regards, fw

from base r documentation:

both [[ , $ select single element of list. main difference $ not allow computed indices, whereas [[ does. x$name equivalent x[["name", exact = false]]. also, partial matching behavior of [[ can controlled using exact argument.

a data.table data.frame, , data.frame list, data.table list. inexact matching $ allowed. that's nice interactive session you're trying explore data, not nice non-interactive code can blow when unexpected happens.

this why it's almost always bad idea use $ subsetting if you're not 100% sure column exists. , then, fall prey typos. instead of dt$name, use dt[["name"]]. won't raise error, return null, easy check. if let go, null cause error down line.


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