Fix subset error when only set select argument

Author: yanboliang

R/pkg/R/DataFrame.R

@@ -1209,7 +1209,11 @@ setMethod("[", signature(x = "DataFrame", i = "Column"),
 #' }
 setMethod("subset", signature(x = "DataFrame"),
           function(x, subset, select, ...) {
-            x[subset, select, ...]
+            if (missing(subset)) {
+                x[, select, ...]
+            } else {
+                x[subset, select, ...]
+            }
           })
 
 #' Select

R/pkg/inst/tests/testthat/test_sparkSQL.R

@@ -799,6 +799,10 @@ test_that("subsetting", {
   expect_equal(count(df6), 1)
   expect_equal(columns(df6), c("name", "age"))
 
+  df7 <- subset(df, select = "name")
+  expect_equal(count(df7), 3)
+  expect_equal(columns(df7), c("name"))
+
   # Test base::subset is working
   expect_equal(nrow(subset(airquality, Temp > 80, select = c(Ozone, Temp))), 68)
 })