x <- seq.Date(as.Date("2009-08-02"), by = "year", length.out = 2)
# "2009-08-02" "2010-08-02"
pretty.dates(x, 12)
#"2009-08-01 GMT" "2009-09-01 GMT" "2009-10-01 GMT" "2009-11-01 GMT" "2009-12-01 GMT" "2010-01-01 GMT" "2010-02-01 GMT" "2010-03-01 GMT" "2010-04-01 GMT" "2010-05-01 GMT" "2010-06-01 GMT" "2010-07-01 GMT" "2010-08-01 GMT" "2010-09-01 GMT"}
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