> On Jan 29, 2016, at 10:30 PM, lily li <chocol...@gmail.com> wrote:
>
> Hi R users,
>
> I have a data frame, and I generate a date column like this:
> df$date = seq(as.Date('2012-01-01'), as.Date('2014-12-31'))
>
> df
> A B C
> 1 2 1
> 2 2 3
> 3 2 4
>
> So the data frame has 4 columns now. But when I want to change the values
> of column A for specific dates, such as 2012-01-01 to 2013-12-31, I use the
> code below:
> df[date >= '2012-01-01'&date <= '2013-12-31']$A =
> df[date >= '2012-01-01'&date <= '2013-12-31']$A +2
>
> But it does not work, the date I generate seems not effective. What is the
> problem? Thanks for your help.
>
You are using "[" incorrectly. You should be passing that logical vector to the
"row-position" of the i,j-form of the `[<-` function. Try instead:
df[date >= '2012-01-01'&date <= '2013-12-31' , ]$A =
df[ date >= '2012-01-01'&date <= '2013-12-31' , ]$A +2
(As it is, I believe you are selecting columns rather than rows.)
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David Winsemius
Alameda, CA, USA
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