[R] Constructing dummy variables for months for a time series object

[Bill.Venables at csiro.au]

The simplest way is probably to generate them as the columns of a
matrix.  Let's suppose you have data from Jan 1991 up to Mar 2008.

> X <- outer(rep(month.abb, length = 16*12+3), month.abb, "==") + 0

> ## the "+ 0" will convert logical to numeric

> dim(X)
[1] 195  12

> dimnames(X)[[2]] <- month.abb
> head(X)
     Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
[1,]   1   0   0   0   0   0   0   0   0   0   0   0
[2,]   0   1   0   0   0   0   0   0   0   0   0   0
[3,]   0   0   1   0   0   0   0   0   0   0   0   0
[4,]   0   0   0   1   0   0   0   0   0   0   0   0
[5,]   0   0   0   0   1   0   0   0   0   0   0   0
[6,]   0   0   0   0   0   1   0   0   0   0   0   0
>  

To get the July indicators, use X[, "Jul"], &c


Bill Venables
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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Megh Dal
Sent: Friday, 25 April 2008 5:40 PM
To: r-help at stat.math.ethz.ch
Subject: [R] Constructing dummy variables for months for a time series
object

I have a TS of monthly observations. 
   
  head(data4)
 1991(1)  1991(2)  1991(3)  1991(4)  1991(5)  1991(6) 
12.00864 11.94203 11.98386 12.01900 12.19226 12.15488 

  Now I want to make 11 dummy variables indicating months. Therefore I
did followings :
   
  For Jan :
  rep(c(rep(0,0), 1, rep(0, 11)), 17)
   
  For Feb :
  rep(c(rep(0,1), 1, rep(0, 10)), 17)
   
  ........ and so on
   
  But my question is there any way to aumate this? Or I have to do the
above thing for all 11 months?

       
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