如何从年/月数值变量 (R) 格式化月变量

Question

I have a vector with numeric (not formated) year/month variable. Consider the vector below for all months of year 2012. How could I create a formated monthly variable from it?

ym <- c(201201,201202,201203,201204,201205,201206,201207,201208,201209,201210,201211,201212)

Answer 1

May be need

library(zoo)
format(as.yearmon(as.character(ym), '%Y%m'), '%b')

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Or in base R

format(as.Date(paste0(ym, '01'), '%Y%m%d'), '%b')

Answer 2

We can use %% , eg,

> month.abb[ym %% 100]
 [1] "Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"