There is probably a more elegant way to do this, but this worked for me:



# a function to identify the first occurrence of a run of values
first <- function(x) {
    l <- length(x)
    c(1, 1-(x[-1]==x[-l]))
    }

# identify the first occurrence of a run of Rev values 
df$frst <- first(df$Rev)

# assign each run a unique value
df$run <- cumsum(df$frst)

# number the elements of each run
df$no.elements <- unlist(lapply(table(df$run), seq))

# identify the first occurrence of FF=0 within each run
first.FF.0 <- tapply(df$FF, df$run, function(x) match(0, x))

# subset the original data frame, selecting those rows that correspond to 
the first occurrence of FF=0 in each run
result <- data.frame(t(sapply(1:max(df$run), function(g) df[df$run==g, 
][first.FF.0[g], ])))

# identify the rows that have bin=0
result$valid <- result$bin==0

# since you only want the "transitions", ignore the first row of results
# the last two columns are the results you want,
# the number of elements that occurred in the valid and non-valid cases
result[-1, ]



df[1:15, ]
   Rev FF bin frst run no.elements
1    1  1  NA    1   1           1
2    1  1   1    0   1           2
3    1  0   1    0   1           3
4    1  1   1    0   1           4
5    1  1   1    0   1           5
6    1  1   1    0   1           6
7    1  1   0    0   1           7
8    1  1   0    0   1           8
9    1  0   1    0   1           9
10   1  1   1    0   1          10
11   2  0   1    1   2           1
12   2  1   1    0   2           2
13   2  1   1    0   2           3
14   2  1   1    0   2           4
15   2  1   0    0   2           5

result[-1, ]
  Rev FF bin frst run no.elements valid
2   2  0   1    1   2           1 FALSE
3   3  0   1    0   3           2 FALSE
4   1  0   0    1   4           1  TRUE
5   2  0   0    0   5           3  TRUE
6   3  0   1    0   6           5 FALSE
7   1  0   1    0   7           4 FALSE
8   2  0   1    0   8           2 FALSE
9   3  0   0    0   9           2  TRUE



Jean



Edward Patzelt <patze003@umn.edu> wrote on 08/22/2011 04:09:55 PM:

> that is exactly correct, assuming we did not start at the beginning,
> but started at the first transition (this is the correct way to 
> think about it)

> On Mon, Aug 22, 2011 at 4:08 PM, Jean V Adams <jvadams@usgs.gov> wrote:
> 
> So, using the full data set, what should the result look like? 
> 
> c(NA, NA,     NA, 3, NA,    NA, NA, 2)     ? 
> 
> Jean 
> 
> Edward Patzelt <patze003@umn.edu> wrote on 08/22/2011 03:58:38 PM:
> 
> > [image removed] 
> > 
> > Re: [R] Counting Elements Conditionally 
> > 
> > Edward Patzelt 
> > 
> > to: 
> > 
> > Jean V Adams 
> > 
> > 08/22/2011 03:58 PM 
> > 
> > Cc: 
> > 
> > r-help 
> > 
> > Awesome, this is close, couple changes.  Below is full data set for 
> > 1 person.  I want the code to look at the first time it sees a 0 in 
> > FF after the transition in Rev.  I then want it to test whether bin 
> > is also a 0.  If and only if this is the first 0 in FF after the 
> > transition, and bin = 0, then count the number of elements between 
> > the transition in Rev and the 0 in FF. 
> > 
> > 
> > structure(list(Rev = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
> > 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 
> > 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 1L, 1L, 
> > 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
> > 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
> > 3L, 3L, 3L, 3L, 3L, 3L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
> > 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
> > 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
> > 3L, 3L, 3L), FF = c(1L, 1L, 0L, 1L, 1L, 1L, 1L, 1L, 0L, 1L, 0L, 
> > 1L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 
> > 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 1L, 1L, 
> > 1L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 0L, 1L, 
> > 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 0L, 1L, 1L, 
> > 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 
> > 0L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 1L, 
> > 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 1L, 1L, 
> > 1L, 1L), bin = c(NA, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 
> > 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 
> > 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 
> > 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 
> > 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 
> > 0, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 
> > 1, 1, 1, 1, 1)), .Names = c("Rev", "FF", "bin"), row.names = c(NA, 
> > -125L), class = "data.frame") 
> > 
> > On Mon, Aug 22, 2011 at 3:57 PM, Jean V Adams <jvadams@usgs.gov> 
wrote: 
> > 
> > > Re: [R] Counting Elements Conditionally 
> > > Jean V Adams 
> > > to: 
> > > Edward Patzelt 
> > > 08/22/2011 03:53 PM 
> > > 
> > > > [R] Counting Elements Conditionally
> > > > Edward Patzelt 
> > > > to:
> > > > r-help
> > > > 08/22/2011 02:33 PM
> > > > 
> > > > R -
> > > > 
> > > > I have 3 variables with data below.  Variable "Rev" is a vector 
that 
> > > changes
> > > > from 1 to 2, 2 to 3, etc....  Variable "FF" is a binary variable 
with 
> > > 1's
> > > > and 0's.  Variable "bin" is a different binary variable with 1's 
and 
> > > 0's.
> > > > 
> > > > I want to calculate the number of elements:
> > > > 
> > > > 1.  Starting with the first element where Rev switches (i.e. 1 to 
2)
> > > > 
> > > > 2.  The number of elements between the transition and the first 0 
in the
> > > > "FF" vector; *when "bin" is also a 0.*
> > > > *
> > > > *
> > > > 3.  I want to do this for each transition in Rev, but ignore all 
> > > elements
> > > > after calculating #2 until another transition has occurred.
> > > > 
> > > > 
> > > > structure(list(Rev = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
> > > > 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L,
> > > > 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L), FF = 
c(0L,
> > > > 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 0L, 1L, 1L,
> > > > 1L, 1L, 0L, 1L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 0L, 0L, 1L, 1L,
> > > > 1L, 1L, 1L, 0L, 1L, 1L, 1L), bin = c(NA, 1, 1, 1, 1, 1, 1, 1,
> > > > 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1,
> > > > 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1)), .Names = c("Rev", "FF", "bin"
> > > > ), row.names = c(NA, -40L), class = "data.frame")
> > > > 
> > > > 
> > > > -- 
> > > > Edward H. Patzelt
> > > > Research Assistant ? TRiCAM Lab
> > > > University of Minnesota ? Psychology/Psychiatry
> > > > VA Medical Center
> > > > Office: S355 Elliot Hall - Twin Cities Campus
> > > > Phone: 612-626-0072  Email: patze003@umn.edu
> > > > 
> > > 
> > > Try this (I'm assuming your data.frame is called "df":
> > > 
> > > 
> > > uR <- unique(df$Rev)
> > > uR0 <- uR*10L
> > > 
> > > first.Rev <- match(uR, df$Rev)
> > > first.Rev0 <- match(uR0, df$Rev * 10L + df$FF)
> > > 
> > > no.elements <- first.Rev0 - first.Rev + 1
> > > 
> > > 
> > > This starts with Rev=1 (rather than Rev=2), but you can get rid 
> of that by 
> > > dropping the first result ...
> > > 
> > > 
> > > no.elements[-1]
> > > 
> > > 
> > > Jean
> > > 
> 
> > Ooops.  Too hasty in my reply.  I missed the part about bin also 
> > being zero.  Try this instead. 
> > 
> > 
> > uR <- unique(df$Rev) 
> > uR00 <- uR*100L 
> > 
> > first.Rev <- match(uR, df$Rev) 
> > first.Rev00 <- match(uR00, df$Rev * 100L + df$FF * 10L + df$bin) 
> > 
> > no.elements <- first.Rev00 - first.Rev + 1 
> > 
> > 
> > Jean 
> > 
> 
> > 
> > -- 
> > Edward H. Patzelt
> > Research Assistant ? TRiCAM Lab
> > University of Minnesota ? Psychology/Psychiatry
> > VA Medical Center
> > Office: S355 Elliot Hall - Twin Cities Campus
> > Phone: 612-626-0072  Email: patze003@umn.edu
> > 
> > Please consider the environment before printing this email
> > www.psych.umn.edu/research/tricam
> 

> 
> -- 
> Edward H. Patzelt
> Research Assistant ? TRiCAM Lab
> University of Minnesota ? Psychology/Psychiatry
> VA Medical Center
> Office: S355 Elliot Hall - Twin Cities Campus
> Phone: 612-626-0072  Email: patze003@umn.edu
> 
> Please consider the environment before printing this email
> www.psych.umn.edu/research/tricam
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