R中带有as.date的新变量

Question

this is head(both$stterm)

 stterm
1 2011-01-19
2 2012-01-19
3 2007-09-01
4 2011-09-01
5 2008-09-01
6 2013-09-01

this is, as I said just part of a dataset I have 4021 observations. I want to create a new column, were each date instead represents a value as follows below.

Variable should be continuous.

I have tested as.date but I just got a column full of NULL then.

Important that it is 2008-09-01 = 8 and not 08

"2007-09-01"=7,
"2008-09-01"=8,
"2009-01-19"=9,
"2009-09-01"=9,
"2010-01-19"=10,
"2010-09-01"=10,
"2011-01-19"=11,
"2011-09-01"=11,
"2012-01-19"=12,
"2012-09-01"=12,
"2013-01-19"=13,
"2013-09-01"=13,
"2014-01-19"=14)

so what I want to do is simply to create a column with the digits instead of the actual dates. the new variable will be called: calenderyear.

I need tips on how to write this in R

Answer 1

You can do this as follows:

require(lubridate)
dat$year <- year(as.Date(dat$stterm))-2000

Result:

> dat
      stterm year
1 2011-01-19   11
2 2012-01-19   12
3 2007-09-01    7
4 2011-09-01   11
5 2008-09-01    8
6 2013-09-01   13

Data:

dat <- read.table(header = TRUE, stringsAsFactors = FALSE, text = " stterm
1 2011-01-19
2 2012-01-19
3 2007-09-01
4 2011-09-01
5 2008-09-01
6 2013-09-01")

Answer 2

Try the lubridate library

install.packages(lubridate)
library(lubridate)
year(ymd(both$stterm))-2000

Answer 3

you can try this

d <- as.Date(c("2007-09-01", "2008-09-01", "2009-01-19", "2009-09-01", "2010-01-19", "2010-09-01", "2011-01-19", "2011-09-01", "2012-01-19", "2012-09-01", "2013-01-19", "2013-09-01", "2014-01-19"), format="%Y-%m-%d")
sub("^0", "", sub("[[:digit:]]{2}([[:digit:]]{2}).*", "\\1", d))
 [1] "7"  "8"  "9"  "9"  "10" "10" "11" "11" "12" "12" "13" "13" "14"

Answer 4

You can try do this using base R: First to reproduce a subset of your dataset:

both <- data.frame( stterm=as.Date(c('2011-01-19','2012-01-19', '2007-09-01','2011-09-01','2008-09-01','2013-09-01')))

both
      stterm
1 2011-01-19
2 2012-01-19
3 2007-09-01
4 2011-09-01
5 2008-09-01
6 2013-09-01

both$calenderyear <- as.numeric(format(both$stterm,"%y"))
both
      stterm calenderyear
1 2011-01-19           11
2 2012-01-19           12
3 2007-09-01            7
4 2011-09-01           11
5 2008-09-01            8
6 2013-09-01           13