[R] how to extract word before /// in a data frame contain many thousands rows.

[Stephen HK Wong]

Dear All,

I appreciate if you can help me out this. I have a data frame contains many thousand of rows, with some rows that has /// symbol,  as shown in in row 2, I want to extract word before ///, such as in this case, CDH23. Many thanks.
Probe.Set.ID            Gene.Symbol
1  1552301_a_at                  CORO6
2  1552436_a_at CDH23 /// LOC100653137
3  1552477_a_at                   IRF6
4  1552685_a_at                  GRHL1
5    1552742_at                  KCNH8
6  1552752_a_at                  CADM2
7    1552799_at                TSNARE1
8  1552897_a_at                  KCNG3
9  1552902_a_at                  FOXP2
10   1552903_at               B4GALNT2


structure(list(Probe.Set.ID = c("1552301_a_at", "1552436_a_at", 
"1552477_a_at", "1552685_a_at", "1552742_at", "1552752_a_at", 
"1552799_at", "1552897_a_at", "1552902_a_at", "1552903_at"), 
    Gene.Symbol = c("CORO6", "CDH23 /// LOC100653137", "IRF6", 
    "GRHL1", "KCNH8", "CADM2", "TSNARE1", "KCNG3", "FOXP2", "B4GALNT2"
    )), .Names = c("Probe.Set.ID", "Gene.Symbol"), row.names = c(NA, 
10L), class = "data.frame")


Stephen HK Wong