dataframe - How can I create a transitions column in R -

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i have state column in dataframe , want create 2 new columns: 1 looks ahead next stage change , 1 looks previous state change. resulting dataframe below:

state coming  previous       a-b     na       a-b     na       a-b     na       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       na      c-a       na      c-a

or maybe better, create 2 transition columns:

state trans1   trans2       a-b     na       a-b     na       a-b     na       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       c-a     na        c-a     na

[edit] changed states named "1" "c" because confusing

let's give dataframe name, 'inp'. use rle function construct 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 able overcome difficulty understanding first request, had persistent difficulty second part.)


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