force class reset

Author: ben-schwen

R/as.data.table.R

@@ -215,7 +215,11 @@ as.data.table.list = function(x,
 
 as.data.table.data.frame = function(x, keep.rownames=FALSE, key=NULL, ...) {
   if (is.data.table(x)) return(as.data.table.data.table(x, key=key)) # S3 is weird, #6739. Also # nocov; this is tested in 2302.{2,3}, not sure why it doesn't show up in coverage.
-  if (!identical(class(x), "data.frame")) return(as.data.table(as.data.frame(x), keep.rownames=keep.rownames, key=key, ...))
+  if (!identical(class(x), "data.frame")) {
+    x = as.data.frame(x)
+    setattr(x,"class","data.frame") # cater for cases when as.data.frame is overridden #6874
+    return(as.data.table(x, keep.rownames=keep.rownames, key=key, ...))
+  }
   if (!isFALSE(keep.rownames)) {
     # can specify col name to keep.rownames, #575; if it's the same as key,
     #   kludge it to 'rn' since we only apply the new name afterwards, #4468

inst/tests/tests.Rraw

@@ -21104,3 +21104,8 @@ DT = data.table(a = 1:5, b = 1:5, x = 1:5)
 test(2309.06, key(as.data.table(DT, key="a")), "a")   
 test(2309.07, key(as.data.table(DT)), NULL)          
 test(2309.08, key(as.data.table(DT, key=NULL)), NULL) 
+
+# as.data.frame(x) does not reset class(x) to "data.frame" #6874
+as.data.frame.no.reset = function(x) x
+DF = structure(list(a = 1:2), class = c("data.frame", "no.reset"), row.names = c(NA, -2L))
+test(2310.01, as.data.table(DF), data.table(a=1:2))