PUB-682: head of empty data frame does not throw

Author: spennihana

R/tests/testdir_jira/runit_pub_682_head_empty_frame.R

@@ -0,0 +1,19 @@
+setwd(normalizePath(dirname(R.utils::commandArgs(asValues=TRUE)$"f")))
+source('../findNSourceUtils.R')
+
+test.head_empty_frame <- function(conn) {
+
+  a_initial = cbind(c(0,0,0,0), c(1,1,1,1)) 
+  # create data frame without col names in R, transfer to h2o (V* names preserved from R) 
+  a.h2o <- as.h2o(conn, a_initial, key="A.hex")
+  
+  # now we'll create an empty b.h2o in h2o 
+  b.h2o = a.h2o[a.h2o$V1==32]
+  
+  head(b.h2o[,1]) 
+  head(b.h2o[1,]) 
+  
+  testEnd()
+}
+
+doTest("Test frame add.", test.head_empty_frame)

src/main/java/water/fvec/Frame.java

@@ -817,6 +817,9 @@ else if (ocols instanceof Frame) {
     else if (orows instanceof long[]) {
       final long CHK_ROWS=1000000;
       long[] rows = (long[])orows;
+      if (this.numRows() == 0) {
+        return this;
+      }
       if( rows.length==0 || rows[0] < 0 ) {
         if (rows[0] < 0) {
           Vec v = (new SelectVec(rows)).doAll(this.anyVec().makeZero()).getResult()._fr.anyVec();