R help - Sep 2007 - Function to get a sequence of months

Hi all,

I am looking for a function for following calculation.

start.month = "July"
end.month = "January"

months = f(start.month, end.month, by=1)

* f is the function that I am looking for.

Actually I want to get months = c("July",
"August",.............."January")

If start.month = 6 and end.month = 1 then I could use (not properly) seq()
function and then I would get month as a vector with elements 6,5,4,3,2, and
1 by choosing "by=-1". Is there any function which can subsitute the
seq()
function in my case?

Regards,

	[[alternative HTML version deleted]]

On 11/09/2007 6:36 AM, Arun Kumar Saha wrote:
> Hi all,
> 
> I am looking for a function for following calculation.
> 
> start.month = "July"
> end.month = "January"
> 
> months = f(start.month, end.month, by=1)
> 
> * f is the function that I am looking for.
> 
> Actually I want to get months = c("July",
"August",.............."January")
> 
> If start.month = 6 and end.month = 1 then I could use (not properly) seq()
> function and then I would get month as a vector with elements 6,5,4,3,2,
and
> 1 by choosing "by=-1". Is there any function which can subsitute
the seq()
> function in my case?
I don't think one already exists, but it's easy to write one:

 > cyclic_seq <- function(from, to, cycle=12) {
+     if (to < from) (from - 1):(to + cycle - 1) %% cycle + 1
+     else from:to
+ }
 > cyclic_seq(5, 1)
[1]  5  6  7  8  9 10 11 12  1
 > cyclic_seq(5, 5)
[1] 5
 > cyclic_seq(5, 6)
[1] 5 6

This makes various assumptions about the inputs (e.g. it would fail on 
cyclic_seq(20, 1) ); you might want to validate the inputs if you're 
giving it to other people.

Duncan Murdoch

Here is a solution using character manipulation.  Noting that month.name
is built into R we paste together the character string:
"January Februrary ... December January ... December"
Then we use perl style ungreedy matching to get the shortest substring
matching the indicated expression then splitting it back apart and taking
the first match:

library(gsubfn)
strapply(paste(rep(month.name, 2), collapse = " "),
"July.*?January",
  ~ strsplit(x, split = " "), perl = TRUE, simplify = c)[[1]]


Here is the result of running it:
> library(gsubfn)
> strapply(paste(rep(month.name, 2), collapse = " "),
"July.*?January",
+   ~ strsplit(x, split = " "), perl = TRUE, simplify = c)[[1]]
[1] "July"      "August"    "September"
"October"   "November"
"December"  "January"


mn2 <- c(month.name, month.name)
strapply(paste(mn2, "July.*January", ~ strsplit(x, split = "
"),
simplify = unlist)

On 9/11/07, Arun Kumar Saha <arun.kumar.saha at gmail.com>
wrote:
> Hi all,
>
> I am looking for a function for following calculation.
>
> start.month = "July"
> end.month = "January"
>
> months = f(start.month, end.month, by=1)
>
> * f is the function that I am looking for.
>
> Actually I want to get months = c("July",
"August",.............."January")
>
> If start.month = 6 and end.month = 1 then I could use (not properly) seq()
> function and then I would get month as a vector with elements 6,5,4,3,2,
and
> 1 by choosing "by=-1". Is there any function which can subsitute
the seq()
> function in my case?
>
> Regards,
>
>        [[alternative HTML version deleted]]
>
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