It sounds like you're just looking for table
and which
:
String <- c("a", "about", "base", "base", "h2o", "h", "yes", "a", "c", "h", "d")
table(String)
# String
# a about base c d h h2o yes
# 2 1 2 1 1 2 1 1
which(String == "a")
# [1] 1 8
nchar(String)
# [1] 1 5 4 4 3 1 3 1 1 1 1
table(String[nchar(String) == 1])
#
# a c d h
# 2 1 1 2