r: convert a string to date

Question

I have a string like that:

And I'd like to convert to Date, like so:

I have tried:df$month_key=as.Date(df$month_key,format="YYYYmm") But it asks for the origin, which we don't need to care about. Is there a way to do that, or maybe add a dash between character 4 and 5 in the whole column? Thanks

See http://stackoverflow.com/questions/13863599/insert-a-character-at-a-specific-location-in-a-string — Wiktor Stribiżew, Aug 18 '16 at 11:13

akrun · Accepted Answer · 2016-08-18T10:48:01.837

We can use sub to create a - between the first 4 characters and the next 2. Match the four characters (.{4}), place it in a capture groups ((...)), followed by the next 2 characters in another capture group, replace it with the backreference for those groups (\\1, \\2) and in between we add the -.

df1$Col <- sub('(.{4})(.{2})', "\\1-\\2", df1$month_key)
df1$Col
#[1] "2016-01" "2016-03" "2016-04" "2016-06" "2015-01"

Another option is substr/paste

with(df1, paste(substr(month_key, 1,4), substr(month_key, 5, 6), sep="-"))

However, a Date class have a day as well. So, to convert the original column to 'Date', we can append with any day, perhaps with 01 and use the format in as.Date

as.Date(paste0(df1$month_key, "01"), "%Y%m%d")

data

df1 <- structure(list(Col = c(201601L, 201603L, 201604L, 201606L, 201501L
 )), .Names = "month_key", class = "data.frame", row.names = c(NA, -5L))

You don't have to convert the string to a date by inserting a hyphen. You can also consider using `zoo`: `library(zoo); as.yearmon("201603", "%Y%m")` (unfortunately, `lubridate` doesn't appear to do this yet). Answers from a different duplicate question: https://stackoverflow.com/questions/6242955/converting-year-and-month-yyyy-mm-format-to-a-date — Dannid, Feb 27 '19 at 18:37

r: convert a string to date

1 Answers1

data