# [R] how to count number of occurrences

William Dunlap wdunlap at tibco.com
Wed Nov 2 19:13:05 CET 2011

```Is the following what you want?  It should give
the number of "X"s immediately preceding each "Y".

> samp <- c("X", "Y", "X", "X", "X", "X", "Y", "Y", "Y", "Y", "X", "X",
"X", "X", "X", "Y", "Y", "Y", "Y", "Y")
> diff((seq_along(samp) - cumsum(samp=="Y"))[samp=="Y"])
[1] 4 0 0 0 5 0 0 0 0

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Sl K
> Sent: Wednesday, November 02, 2011 9:55 AM
> To: r-help at r-project.org
> Subject: [R] how to count number of occurrences
>
> Dear R users,
>
> I have this data frame,
>            y samp
> 8  0.03060419    X
> 18 0.06120838    Y
> 10 0.23588374    X
> 3  0.32809965    X
> 1  0.36007100    X
> 7  0.36730571    X
> 20 0.47176748    Y
> 13 0.65619929    Y
> 11 0.72014201    Y
> 17 0.73461142    Y
> 6  0.76221313    X
> 2  0.77005691    X
> 4  0.92477243    X
> 9  0.93837591    X
> 5  0.98883581    X
> 16 1.52442626    Y
> 12 1.54011381    Y
> 14 1.84954487    Y
> 19 1.87675183    Y
> 15 1.97767162    Y
>
> and I am trying to find the number of X's that occur before ith Y occurs.
> For example, there is 1 X before the first Y, so I get 1. There are 4 X's
> before the second Y, so I get 4, there is no X between second and third Y,
> so I get 0 and so on. Any hint to at least help me to start this will be
> appreciated. Thanks a lot!
>
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>
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