R help - May 2008 - recode involving a count rule

Hello, R-helpers.

I have a data frame below called df. I want to add a variable c, based on
the following logic:

if df$a < 5 then the first two times this condition is met place a 1 in c,
the next two times this condition is met place a 2 in c and when the
condition is not met let c equal df$b.  The result would look like, dfnew,
shown below.


a <- rep(c(3,5,7), 4)
b <- rep(c(NA,1,2), 4)
df <- data.frame(a,b)
> df
   a  b
1  3 NA
2  5  1
3  7  2
4  3 NA
5  5  1
6  7  2
7  3 NA
8  5  1
9  7  2
10 3 NA
11 5  1
12 7  2

c <- c(1 , 1,  2, 1, 1,  2, 2,  1,  2, 2,  1,  2)
dfnew <- data.frame(a, b,c)
> dfnew
   a  b c
1  3 NA 1
2  5  1 1
3  7  2 2
4  3 NA 1
5  5  1 1
6  7  2 2
7  3 NA 2
8  5  1 1
9  7  2 2
10 3 NA 2
11 5  1 1
12 7  2 2

Thanks
Greg
R 2.7 XP

-- 
Gregory L. Blevins
Office 952 944-5743
Cell 612 251 0232
gregblev@gmail.com

	[[alternative HTML version deleted]]

This should do what you want -- not sure what happens after the 4th less than 5.
> a <- rep(c(3,5,7), 4)
> b <- rep(c(NA,1,2), 4)
> df <- data.frame(a,b)
> # determine which ones are < 5 and count the occurances
> less.5 <- cumsum(df$a < 5)
> # create new value
> df$c <- ifelse(df$a < 5, (less.5 + 1) %/% 2, df$b)
> df
   a  b c
1  3 NA 1
2  5  1 1
3  7  2 2
4  3 NA 1
5  5  1 1
6  7  2 2
7  3 NA 2
8  5  1 1
9  7  2 2
10 3 NA 2
11 5  1 1
12 7  2 2


On Sat, May 3, 2008 at 3:43 PM, Greg Blevins <gregblev at gmail.com>
wrote:
> Hello, R-helpers.
>
> I have a data frame below called df. I want to add a variable c, based on
> the following logic:
>
> if df$a < 5 then the first two times this condition is met place a 1 in
c,
> the next two times this condition is met place a 2 in c and when the
> condition is not met let c equal df$b.  The result would look like, dfnew,
> shown below.
>
>
> a <- rep(c(3,5,7), 4)
> b <- rep(c(NA,1,2), 4)
> df <- data.frame(a,b)
>
> > df
>   a  b
> 1  3 NA
> 2  5  1
> 3  7  2
> 4  3 NA
> 5  5  1
> 6  7  2
> 7  3 NA
> 8  5  1
> 9  7  2
> 10 3 NA
> 11 5  1
> 12 7  2
>
> c <- c(1 , 1,  2, 1, 1,  2, 2,  1,  2, 2,  1,  2)
> dfnew <- data.frame(a, b,c)
> > dfnew
>   a  b c
> 1  3 NA 1
> 2  5  1 1
> 3  7  2 2
> 4  3 NA 1
> 5  5  1 1
> 6  7  2 2
> 7  3 NA 2
> 8  5  1 1
> 9  7  2 2
> 10 3 NA 2
> 11 5  1 1
> 12 7  2 2
>
> Thanks
> Greg
> R 2.7 XP
>
> --
> Gregory L. Blevins
> Office 952 944-5743
> Cell 612 251 0232
> gregblev at gmail.com
>
>        [[alternative HTML version deleted]]
>
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>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?