[R] about change columns for specific rows

[David Winsemius]

> On Jan 29, 2016, at 10:30 PM, lily li <chocold12 at 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