Rilcon42 - 2 months ago 6x
R Question

# counting lengths between alternating columns

I am trying to figure out how to count the number of rows from when one column says True to when the other column says True. I attempted to use run length encoding but couldnt figure out how to get the alternating values form each column.

``````set.seed(42)
s<-sample(c(0,1,2,3),500,replace=T)
isOverbought<-s==1
isOverSold<-s==0
res<-rle(isOverSold)
tt<-res[res\$values==0] #getting when Oversold is true

[1,]        FALSE      FALSE
[2,]        FALSE      FALSE
[3,]         TRUE      FALSE <-starting condition is overbought
[4,]        FALSE      FALSE
[5,]        FALSE      FALSE
[6,]        FALSE      FALSE
[7,]        FALSE      FALSE
[8,]        FALSE       TRUE <-is oversold. length from overbought to oversold = 5
[9,]        FALSE      FALSE
[10,]        FALSE      FALSE
[11,]         TRUE      FALSE <- is overbought. length from oversold to overbought = 3
[12,]        FALSE      FALSE
[13,]        FALSE      FALSE
[14,]         TRUE      FALSE
[15,]         TRUE      FALSE
[16,]        FALSE      FALSE
[17,]        FALSE      FALSE
[18,]        FALSE       TRUE <-is oversold. length from overbought to oversold = 7
[19,]         TRUE      FALSE <- is overbought. length from oversold to overbought = 1
[20,]        FALSE      FALSE
``````

GOAL

``````overboughtTOoversold oversoldTOoverbought
5                     3
7                     1
``````

This is sufficient to solve your problem.

``````## `a` to `b`
a2b <- function (a, b) {
x <- which(a)    ## position of `TRUE` in `a`
y <- which(b)    ## position of `TRUE` in `b`
z <- which(a | b)   ## position of all `TRUE`
end <- match(y, z)    ## match for end position
start <- c(1L, end[-length(end)] + 1L)    ## start position
valid <- end > start  ## remove cases with `end = start`
z[end[valid]] - z[start[valid]]
}

## cross `a` and `b`
axb <- function (a, b) {
if (any(a & b))
stop ("Invalid input! `a` and `b` can't have TRUE at the same time!")
x <- a2b(a, b); y <- a2b(b, a)
if (which(a)[1L] < which(b)[1L]) cbind(a2b = x, b2a = c(NA_integer_, y))
else cbind(a2b = c(NA_integer_, x), b2a = y)
}
``````

For your `isOverbought` and `isOverSold`, we obtain:

``````result <- axb(isOverbought, isOverSold)

Since `isOverbought` has the first `TRUE` before `isOverSold`, the first element of the 2nd column is `NA`.