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I'm trying to build folders to store data pulls. I want to label the folders with the day of that data in the pull.
Ex. I pull 5 days ago data from mysql i want to name the folder the date from 5 days ago.
MySQL can easily handle date arithmetic. I'm not sure exactly how R does it. Should i just subtract the appropriate number of seconds in POSIXct and then convert to POSIXlt to name the folder MM_DD_YYYY?
Or is there a better way?
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Enter the number of days to add or subtract in column B. You can enter a negative number to subtract days from your start date, and a positive number to add to your date. In cell C2, enter =A2+B2, and copy down as needed.
Therefore, you can add or subtract days as easy as adding or minus the number of days in Excel. 1. Select a blank cell you will place the calculating result, type the formula =A2+10, and press the Enter key. Note: For subtracting 10 days from the date, please use this formula =A2–10.
Type '=' and select the first cell of the column containing the dates you want to add days to (cell A2). Next, type '+' followed by the number of days you want to add. So, if you want to add 15 days, type '+15' in the same cell. This means, your cell H2 should have the formula =A2+15.
Just subtract a number:
> as.Date("2009-10-01") [1] "2009-10-01" > as.Date("2009-10-01")-5 [1] "2009-09-26" Since the Date class only has days, you can just do basic arithmetic on it.
If you want to use POSIXlt for some reason, then you can use it's slots:
> a <- as.POSIXlt("2009-10-04") > names(unclass(as.POSIXlt("2009-10-04"))) [1] "sec" "min" "hour" "mday" "mon" "year" "wday" "yday" "isdst" > a$mday <- a$mday - 6 > a [1] "2009-09-28 EDT" The answer probably depends on what format your date is in, but here is an example using the Date class:
dt <- as.Date("2010/02/10") new.dt <- dt - as.difftime(2, unit="days") You can even play with different units like weeks.
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