[R] data frame question

[Andras Farkas]

thank you both... assumption is in fact that a and b are always the same length... these work for me well...

much appreciate it... 
Andras 


On Sunday, August 6, 2017 12:14 PM, Ulrik Stervbo <ulrik.stervbo at gmail.com> wrote:



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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>
>
>______________________________________________
>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.
>