[R] data frame question

[Ulrik Stervbo]

Hi Andreas,

assuming that the increment is always indicated by the same value (in your
example 0), this could work:

df$a <- cumsum(seq_along(df$b) %in% which(df$b == 0))
df

HTH,
Ulrik

On Sun, 6 Aug 2017 at 18:06 Bert Gunter <bgunter.4567 at gmail.com> wrote:

> Your specification is a bit unclear to me, so I'm not sure the below
> is really what you want. For example, your example seems to imply that
> a and b must be of the same length, but I do not see that your
> description requires this. So the following may not be what you want
> exactly, but one way to do this(there may be cleverer ones!) is to
> make use of ?rep. Everything else is just fussy detail. (Your example
> suggests that you should also learn about ?seq. Both of these should
> be covered in any good R tutorial, which you should probably spend
> time with if you haven't already).
>
> Anyway...
>
> ## WARNING: Not thoroughly tested! May (probably :-( ) contain bugs.
>
> f <- function(x,y,switch_val =0)
> {
>    wh <- which(y == switch_val)
>    len <- length(wh)
>    len_x <- length(x)
>    if(!len) x
>    else if(wh[1] == 1){
>       if(len ==1) return(rep(x[1],len_x))
>       else {
>          wh <- wh[-1]
>          len <- len -1
>       }
>    }
>    count <- c(wh[1]-1,diff(wh))
>    if(wh[len] == len_x) count<- c(count,1)
>    else count <- c(count, len_x - wh[len] +1)
>    rep(x[seq_along(count)],times = count)
> }
>
> > a <- c(1:5,1:8)
> > b <- c(0:4,0:7)
> > f(a,b)
>  [1] 1 1 1 1 1 2 2 2 2 2 2 2 2
>
>
>
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
>
> On Sun, Aug 6, 2017 at 4:10 AM, Andras Farkas via R-help
> <r-help at r-project.org> wrote:
> > Dear All,
> >
> > wonder if you have thoughts on the following:
> >
> > let us say we have:
> >
> >
> df<-data.frame(a=c(1,2,3,4,5,1,2,3,4,5,6,7,8),b=c(0,1,2,3,4,0,1,2,3,4,5,6,7))
> >
> >
> >  I would like to rewrite values in column name "a" based on values in
> column name "b", where based on a certain value of column "b" the next
> value of column 'a' is prompted, in other words would like to have this as
> a result:
> >
> >
> df<-data.frame(a=c(1,1,1,1,1,2,2,2,2,2,2,2,2),b=c(0,1,2,3,4,0,1,2,3,4,5,6,7))
> >
> >
> > where at the value of 0 in column 'b' the number in column a changes
> from 1 to 2. From the first zero value of column 'b' and until the next
> zero in column 'b' the numbers would not change in 'a', ie: they are all 1
> in my example... then from 2 it would change to 3 again as 'b' will have
> zero again in a row, and so on.. Would be grateful for a solution that
> would allow me to set the values (from 'b') that determine how the values
> get established in 'a' (ie: lets say instead of 0 I would want 3 being the
> value where 1 changes to 2 in 'a') and that would be flexible to take into
> account that the number of rows and the number of time 0 shows up in a row
> in column 'b' may vary...
> >
> > much appreciate your thoughts..
> >
> > Andras
> >
> > ______________________________________________
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> > 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.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

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