CODEWITHSUNDEEP
rdataframe
Robert
Robert

Reputation: 1028

How can I create a transitions column in R

I have a state column in a dataframe and I want to create two new columns: One that looks ahead to the next stage change and one that looks back to the previous state change. So the resulting dataframe will look like below:

state coming  previous
  a     a-b     NA
  a     a-b     NA
  a     a-b     NA
  a     a-b     NA
  b     b-c     a-b
  b     b-c     a-b
  b     b-c     a-b
  c     c-a     b-c
  c     c-a     b-c
  c     c-a     b-c
  a     NA      c-a
  a     NA      c-a

Or maybe even better, but now you just create two transition columns:

state trans1   trans2
  a     a-b     NA
  a     a-b     NA
  a     a-b     NA
  a     a-b     NA
  b     a-b     b-c 
  b     a-b     b-c
  b     a-b     b-c
  c     c-a     b-c
  c     c-a     b-c
  c     c-a     b-c
  a     c-a     NA 
  a     c-a     NA

[Edit] changed states named "1" to "c" because it was confusing

Upvotes: 0

Views: 113

Answers (2)

Robert
Robert

Reputation: 1028

Thanks to DWin's answer I found the answer to the second part om my question myself. Here's the complete code to create a dataframe with a transitions column:

state = rep(c('a','b','c','a'), c(4,3,3,2))
inp=data.frame(state, vals=rnorm(12))
runinps=rle(as.character(inp$state)) # doesn't work without as.character

(rs <- runinps$values)
(ls=runinps$lengths)

(inp$coming <- rep( c( paste( rs[-length(rs)], rs[-1], sep="-"), NA), ls ))
(inp$previous <-rep( c( NA, paste(rs[-length(rs)], rs[-1], sep="-")), ls ))

# Create the first transitions column
(reps=rep(1:(length(ls)/2),each=2))
(ls2=as.vector(tapply(ls , reps, sum)))
seqRs=seq(from=1,to=length(rs),by=2)
(inp$trans <- rep(paste( rs[seqRs], rs[seqRs+1], sep="-"), ls2 ))

# Create the second transitions column
reps=c(reps[-1], max(reps)+1)
(ls2=as.vector(tapply(ls , reps, sum)))
seqRs=seq(from=2,to=length(rs)-1,by=2)
(inp$trans2 <- rep(c(NA, paste( rs[seqRs], rs[seqRs+1], sep="-"), NA), ls2 ))

# some last commands to create one transition column
inp2=subset(inp,!is.na(inp$trans2))
inp2$trans=inp2$trans2
inp=rbind(inp,inp2)
inp$trans2<-NULL

Upvotes: 0

IRTFM
IRTFM

Reputation: 263451

Let's give that dataframe a name, say 'inp'. Use the rle function to construct the sequence of "states":

> rle(inp$state)
Run Length Encoding
  lengths: int [1:4] 4 3 3 2
  values : chr [1:4] "a" "b" "1" "a"

runinp <- rle(inp$state)$values
paste( runinp[-length(runinp)], runinp[-1], sep="-")
# [1] "a-b" "b-1" "1-a"
inp$coming <- rep( c( paste( runinp[-length(runinp)], runinp[-1], sep="-"), NA), 
                    rle(inp$state)$lengths )
inp$coming
# [1] "a-b" "a-b" "a-b" "a-b" "b-1" "b-1" "b-1" "1-a" "1-a" "1-a" NA    NA   

inp$previous <- 
 rep( c( NA_character_, paste(runinp[-1], runinp[-length(runinp)], sep="-")), 
      rle(inp$state)$lengths )
inp$previous
 [1] NA    NA    NA    NA    "b-a" "b-a" "b-a" "1-b" "1-b" "1-b" "a-1" "a-1"

(I was able to overcome my difficulty with understanding your first request, but had persistent difficulty with the second part.)

Upvotes: 1

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