following sequence of A-B-C-D-E-F. How to proceed using R

Question

I have 1 data frame, I want to to go from A to F by following sequence of A-B-C-D-E-F. How to proceed using R.

> m
 V1 V2 V3
1  A  B 0.1
2  B  C 0.2
3  C  D 0.3
4  D  E 0.2
5  E  F 0.5

Answer 1

The way I understand your comments, the relationship between A and F is the product of m$V3 between their rows.

af <- function(from, to){
    x <- which(m$V1 == from)
    y <- which(m$V2 == to)
    return(prod(m$V3[x:y]))
}

 af("A", "F")
[1] 6e-04

Then, F = A * 0.0006.

To generalize to any sequence and any row order in the table, we first define the sequence.

sq <- c("A", "B", "C", "D", "E", "F") # or LETTERS[1:6] in this case

Within the function, we select the respective rows as those, where both columns V1 and V2 contain sequence conditions that match the specification.

af2 <- function(from, to){
    cond <- sq[which(sq == from):which(sq == to)]
    x <- m$V1 %in% cond & m$V2 %in% cond
    return(prod(m$V3[x]))
}

Test

Using the original matrix, both functions provide identical results.

af("B","E")
[1] 0.012
af2("B","E")
[1] 0.012

When we randomise row order, only the second function returns the correct result.

set.seed(123456)
m <- m[sample(1:5),]
m
  V1 V2  V3
4  D  E 0.2
5  E  F 0.5
2  B  C 0.2
1  A  B 0.1
3  C  D 0.3

af("B","E")
[1] 0.02
af2("B","E")
[1] 0.012