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R/data.table.R

@@ -2842,6 +2842,7 @@ setDT = function(x, keep.rownames=FALSE, key=NULL, check.names=FALSE) {
   }
   # check no matrix-like columns, #3760. Other than a single list(matrix) is unambiguous and depended on by some revdeps, #3581
   if (length(x)>1L) {
+    # for some reason, this can't be cols_with_dims(x), or test 510 will break (no longer emit an .internal.selfref warning). this should be investigated.
     idx = vapply_1i(x, function(xi) length(dim(xi)))>1L
     if (any(idx))
       warningf("Some columns are a multi-column type (such as a matrix column): %s. setDT will retain these columns as-is but subsequent operations like grouping and joining may fail. Please consider as.data.table() instead which will create a new column for each embedded column.", brackify(which(idx)))