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I'm trying to create a fiscal year variable called 'period', which will run from September through August for six years. My data frame 'dat' is structured as follows:

'data.frame':   52966 obs. of  4 variables:
 $ userid       : int  96 96 96 101 101 101 101 101 101 101 ...
 $ comment.year : int  2008 2009 2009 2008 2008 2008 2008 2008 2008 2009 ...
 $ comment.month: int  7 3 8 7 8 9 10 11 12 1 ...
 $ num.comments : int  1 1 1 33 51 16 27 29 40 39 ...

I get this error message: Error: unexpected '=' in "dat$period[comment.year=2008 & comment.month=" when I run the following code. I've experimented with double equal signs and putting the month and year integers in quotes, but no success. I'm also wondering if there's a simpler way to do the recode. Since I'm dealing with 6 years, my approach takes 72 lines. 

dat$period[comment.year=2008 & comment.month=9]<-"1"     
dat$period[comment.year=2008 & comment.month=10]<-"1"                 
dat$period[comment.year=2008 & comment.month=11]<-"1" 
dat$period[comment.year=2008 & comment.month=12]<-"1"
dat$period[comment.year=2009 & comment.month=1]<-"1"
dat$period[comment.year=2009 & comment.month=2]<-"1"
dat$period[comment.year=2009 & comment.month=3]<-"1"
dat$period[comment.year=2009 & comment.month=4]<-"1"
dat$period[comment.year=2009 & comment.month=5]<-"1"
dat$period[comment.year=2009 & comment.month=6]<-"1"
dat$period[comment.year=2009 & comment.month=7]<-"1"
dat$period[comment.year=2009 & comment.month=8]<-"1"
dat$period[comment.year=2009 & comment.month=9]<-"2"
dat$period[comment.year=2009 & comment.month=10]<-"2"                     
dat$period[comment.year=2009 & comment.month=11]<-"2" 
dat$period[comment.year=2009 & comment.month=12]<-"2"
user3614783
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    To make it easier to [reproduce](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) your problem, gives us a `dput` rather than a `str()`. And since you want to test for equality rather than assign, use `==` in your indexing (ie, `dat$period[comment.year==2008 & comment.month==9]<-"1"`) – MrFlick Sep 20 '14 at 03:10
  • Thanks, didn't know about dput. Very useful. I tried dat$period[comment.year==2008 & comment.month==9]<-"1", but got Error in dat$period[comment.year == 2008 & comment.month == 9] <- "1" : object 'comment.year' not found – user3614783 Sep 20 '14 at 11:35
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    Actually it should have been `dat$period[dat$comment.year==2008 & dat$comment.month==9]<-"1"` – MrFlick Sep 20 '14 at 13:41

3 Answers3

2

Rather than doing a bunch of partial assignments, why not just calculate the different in years with a bonus bump for months >=9?

#sample data
dat<-data.frame(
    comment.year=rep(2009:2011, each=12), 
    comment.month=rep(1:12, 3)
)[-(1:8), ]

#assign new period
dat$period<- dat$comment.year-min(dat$comment.year) + ifelse(dat$comment.month>=9,1,0)

which gives you

   comment.year comment.month period
9          2009             9      1
10         2009            10      1
11         2009            11      1
12         2009            12      1
13         2010             1      1
14         2010             2      1
15         2010             3      1
16         2010             4      1
17         2010             5      1
18         2010             6      1
19         2010             7      1
20         2010             8      1
21         2010             9      2
22         2010            10      2
23         2010            11      2
24         2010            12      2
25         2011             1      2
26         2011             2      2
27         2011             3      2
28         2011             4      2
29         2011             5      2
30         2011             6      2
31         2011             7      2
32         2011             8      2
33         2011             9      3
34         2011            10      3
35         2011            11      3
36         2011            12      3

If you want to make sure to start at a certain user, you can use 2009 rather than min(dat$comment.year).

MrFlick
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  • Thanks, this works beautifully, but I don't understand how the ifelse portion works. I know that 9 refers to September, the start of each period, but not clear about the rest of the expression. – user3614783 Sep 20 '14 at 14:25
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Using MrFlick's sample data: 

dat$period = rep(1:3, each=12)[1:28]
dat
   comment.year comment.month period
9          2009             9      1
10         2009            10      1
11         2009            11      1
12         2009            12      1
13         2010             1      1
14         2010             2      1
15         2010             3      1
16         2010             4      1
17         2010             5      1
18         2010             6      1
19         2010             7      1
20         2010             8      1
21         2010             9      2
22         2010            10      2
23         2010            11      2
24         2010            12      2
25         2011             1      2
26         2011             2      2
27         2011             3      2
28         2011             4      2
29         2011             5      2
30         2011             6      2
31         2011             7      2
32         2011             8      2
33         2011             9      3
34         2011            10      3
35         2011            11      3
36         2011            12      3
>

Can easily be extended to your data.

rnso
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0

I guess you could also try (Using @MrFlick's data)

set.seed(42)
dat1 <- dat[sample(1:nrow(dat)),]
dat<- within(dat, {period<- as.numeric(factor(comment.year))
              period[comment.month <9] <- period[comment.month <9] -1})

 dat
 #        comment.year comment.month period
 #9          2009             9      1
 #10         2009            10      1
 #11         2009            11      1
 #12         2009            12      1
 #13         2010             1      1
 #14         2010             2      1
 #15         2010             3      1
 #16         2010             4      1
 #17         2010             5      1
 #18         2010             6      1
 #19         2010             7      1
 #20         2010             8      1
 #21         2010             9      2
 #22         2010            10      2
 #23         2010            11      2
 #24         2010            12      2
 #25         2011             1      2
 #26         2011             2      2
 #27         2011             3      2
 #28         2011             4      2
 #29         2011             5      2
 #30         2011             6      2
 #31         2011             7      2
 #32         2011             8      2
 #33         2011             9      3
 #34         2011            10      3
 #35         2011            11      3
 #36         2011            12      3

Using the unordered dat1

 within(dat1, {period<- as.numeric(factor(comment.year)); period[comment.month <9] <- period[comment.month <9] -1})[,3]
 #[1] 3 3 1 2 2 1 2 1 2 2 1 2 2 1 1 2 2 1 1 1 3 1 2 1 2 1 2 3

Crosschecking the results with @MrFlick's method

 dat1$comment.year-min(dat1$comment.year) + ifelse(dat1$comment.month>=9,1,0)
 # [1] 3 3 1 2 2 1 2 1 2 2 1 2 2 1 1 2 2 1 1 1 3 1 2 1 2 1 2 3
akrun
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