在 R 中将字符串转换为日期格式

Question

I'm trying to convert a string into a date format "yyy-mm-dd" in R programming using below steps:

date<- as.Date(S, "%Y- %m- %d")

where S is a vector containing a string value "15081022"

But above method is not giving an output in the format yyy-mm-dd.

Can someone advise the correct command for this

Answer 1

The as.Date() function will convert a string into date format, and the format of the output will always be in yyyy-mm-dd format in R (ISO 8601). The format argument in the as.Date() function is to specify the date format of the string input. I remember I initially thought it was specifying the output format, but it's the input format (you can change the output format with a subsequent format() function, however this will convert it back to a string).

Your string looks to be in ddmmyyyy ( %d%m%Y ) format, this should be what you specify as the format argument in as.Date() . Your format does not include hyphens, so the format argument should also not include hyphens. Note that ddmmyyyy , dd-mm-yyyy , dd/mm/yyyy , dd.mm.yyyy are all different date formats, even though the day, month and year are in the same order, they would be converted to date with formats %d%m%Y , %d-%m-%Y , %d/%m/%Y , and %d.%m.%Y , respectively.

Further advice on working with dates and times is available in the relevant chapters of R for Data Science by Wickham & Grolemund and The R Cookbook by Teetor & Long.