[R] converting time format

Jim Lemon drjimlemon at gmail.com
Wed Feb 22 22:10:47 CET 2017

Hi Lily.
Two problems. You have named the month field "mon" and then refer to
it as "month". Second, as the resolution of as.Date is days, it can't
produce a valid date without specifying the day. Thus:

# make each day the first day of the month
 as.Date(paste(df.count.mon$year, df.count.mon$mon,1),
 '%Y %m %d')
   count year mon       time
1     22 2014   1 2014-01-01
2     12 2014   2 2014-02-01
You will get values, but I don't think they are the ones you want.


On Thu, Feb 23, 2017 at 6:33 AM, lily li <chocold12 at gmail.com> wrote:
> Hi R users,
> I have a dataframe, with year, month, day, and other variables. I wanted to
> calculated monthly values of the variables. For example, there is one
> variable called 'count'. I use the code below to convert daily data to
> monthly data.
> df.count.mon = aggregate(count ~ year+month, data= df, sum)
> The new dataframe has three columns: year, month, and count. Now I want to
> add one more column as 'time', which has the format 'yyyy-mm'. I use the
> code below but the new column has all NA values. What is the problem and
> how to solve it?
> df.count.mon$time = as.Date(paste(df.count.mon$year, df.count.mon$month),
> '%Y %m')
> I had experience to add one more column with the format 'yyyy-mm-dd', which
> works, but not with monthly format. Thanks for your help.
>         [[alternative HTML version deleted]]
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