Finding the column index where a row changes values in R dataframe/Datatable -

suppose have following dataframe:

df <- data.frame(col1=c(2,2,1),col2=c(2,7,5),col3=c(9,6,4))

i know 2 things:

how can field stating index of column row changes values. hence, first row we'd 1 , 3, , second , third rows, 1, 2 , 3.
how field of "before , after"? first case, 2 -> 9, second , third, 2->7, 7-> 6 , 1 ->5, 5->4, respectively.

what this:

x <- sapply(1:ncol(df), function(x) rle(df[x,])$values)

output of x:

[[1]]   col2 col3 1    2    9  [[2]]   col1 col2 col3 2    2    7    6  [[3]]   col1 col2 col3 3    1    5    4

then if you'd full range of before/after values, use:

lapply(x,function(i) paste0(i,collapse="->"))  [[1]] [1] "2->9"  [[2]] [1] "2->7->6"  [[3]] [1] "1->5->4"

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