Changing date format in R

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There are two steps here:

  • Parse the data. Your example is not fully reproducible, is the data in a file, or the variable in a text or factor variable? Let us assume the latter, then if you data.frame is called X, you can do
 X$newdate <- strptime(as.character(X$date), "%d/%m/%Y")

Now the newdate column should be of type Date.

  • Format the data. That is a matter of calling format() or strftime():
 format(X$newdate, "%Y-%m-%d")

A more complete example:

R> nzd <- data.frame(date=c("31/08/2011", "31/07/2011", "30/06/2011"), 
+                    mid=c(0.8378,0.8457,0.8147))
R> nzd
        date    mid
1 31/08/2011 0.8378
2 31/07/2011 0.8457
3 30/06/2011 0.8147
R> nzd$newdate <- strptime(as.character(nzd$date), "%d/%m/%Y")
R> nzd$txtdate <- format(nzd$newdate, "%Y-%m-%d")
R> nzd
        date    mid    newdate    txtdate
1 31/08/2011 0.8378 2011-08-31 2011-08-31
2 31/07/2011 0.8457 2011-07-31 2011-07-31
3 30/06/2011 0.8147 2011-06-30 2011-06-30
R>

The difference between columns three and four is the type: newdate is of class Date whereas txtdate is character.

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