R help - Feb 2010 - sum sections of data of different lengths from within a data frame

Dear R Help:

I am trying to sum data from one column in a dataframe based on a value in
another. I do not know how to do this easily in R.
For example:

Col A  Col B
1        0
3        0
2        1
2        0
1        0
4        0
1        1
9        1
3        0
5        0
2        1

I would like to cumsum the values in Col A for all rows where Col B is 0, and a
value of 1 in Col B will reset the sum and give a value of 0.001. Thus, for this
table I would like an output of 1, 4, 0.001, 2, 3, 7, 0.001, 0.001, 3, 8, 0.001.
I tried using a For loop, but that summed all the Col A values together. I need
something that does
For (i in 1:length(df$Col B))
{
IF{Col B == 0, cumsum(Col A) "until" Col B == 1, else 0.001}
}
I don't know how to use "until" in R.
Any help would be greatly appreciated!
Kara

WIll this do it for you:
> x <- read.table(textConnection("ColA  ColB
+ 1        0
+ 3        0
+ 2        1
+ 2        0
+ 1        0
+ 4        0
+ 1        1
+ 9        1
+ 3        0
+ 5        0
+ 2        1"), header=TRUE)
> closeAllConnections()
> x.s <- split(x, cumsum(x$ColB))
> x.l <- do.call(rbind, lapply(x.s, function(.grp){
+     newdata <- cbind(.grp, sum=cumsum((.grp$ColB == 0) * .grp$ColA))
+     newdata$sum[newdata$ColB == 1] <- .001
+     newdata
+ }))
>
> x.l
     ColA ColB   sum
0.1     1    0 1.000
0.2     3    0 4.000
1.3     2    1 0.001
1.4     2    0 2.000
1.5     1    0 3.000
1.6     4    0 7.000
2       1    1 0.001
3.8     9    1 0.001
3.9     3    0 3.000
3.10    5    0 8.000
4       2    1 0.001
>

On Tue, Feb 9, 2010 at 9:06 PM, Kara Przeczek <przeczek at unbc.ca>
wrote:
> Dear R Help:
>
> I am trying to sum data from one column in a dataframe based on a value in
another. I do not know how to do this easily in R.
> For example:
>
> Col A ?Col B
> 1 ? ? ? ?0
> 3 ? ? ? ?0
> 2 ? ? ? ?1
> 2 ? ? ? ?0
> 1 ? ? ? ?0
> 4 ? ? ? ?0
> 1 ? ? ? ?1
> 9 ? ? ? ?1
> 3 ? ? ? ?0
> 5 ? ? ? ?0
> 2 ? ? ? ?1
>
> I would like to cumsum the values in Col A for all rows where Col B is 0,
and a value of 1 in Col B will reset the sum and give a value of 0.001. Thus,
for this table I would like an output of 1, 4, 0.001, 2, 3, 7, 0.001, 0.001, 3,
8, 0.001.
> I tried using a For loop, but that summed all the Col A values together. I
need something that does
> For (i in 1:length(df$Col B))
> {
> IF{Col B == 0, cumsum(Col A) "until" Col B == 1, else 0.001}
> }
> I don't know how to use "until" in R.
> Any help would be greatly appreciated!
> Kara
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


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

What is the problem that you are trying to solve?

Dear Kara,

Did you bother to test your code? You say your code actually did some
summing, but you didn't include any working example of that code. Did you
bother to read the posting guide?

(1) TRY to reference Col A (including space, as you indicated) in
df.
>names(df)<-c("Col A", "Col B") #space
>df$Col A
>df$"Col A"
>names(df)<-c("ColA", "ColB") # no space
>df$ColA
(2) READ about flow control. Do you see 'until' mentioned
anywhere?
>?Control 
(3) Do YOUR OWN working example. TRY to write a for loop with a capital F,
for example...
>For(i in 1:10){print(i)} 
>for(i in 1:10){print(i)}
(4) OBSERVE what "actually" happens when you take the length of your
data
frame. Does it make any sense?
>length(df)
>ncol(df)
>dim(df)
Crawl, then walk. Don't be lazy.

KeithC.

-----Original Message-----
From: Kara Przeczek [mailto:przeczek at unbc.ca] 
Sent: Tuesday, February 09, 2010 7:07 PM
To: r-help at r-project.org
Subject: [R] sum sections of data of different lengths from within a data
frame

Dear R Help:

I am trying to sum data from one column in a dataframe based on a value in
another. I do not know how to do this easily in R.
For example:

Col A  Col B
1        0
3        0
2        1
2        0
1        0
4        0
1        1
9        1
3        0
5        0
2        1

I would like to cumsum the values in Col A for all rows where Col B is 0,
and a value of 1 in Col B will reset the sum and give a value of 0.001.
Thus, for this table I would like an output of 1, 4, 0.001, 2, 3, 7, 0.001,
0.001, 3, 8, 0.001.
I tried using a For loop, but that summed all the Col A values together. I
need something that does For (i in 1:length(df$Col B)) { IF{Col B == 0,
cumsum(Col A) "until" Col B == 1, else 0.001} } I don't know how
to use
"until" in R.
Any help would be greatly appreciated!
Kara