Question

I´d like to count the number of changes of binary factor variable. This variable can change from time to time back and forth multiple times for every user id. Now I´d like to count he number of changes per user id to this variable over a given timespan.

The data is sorted by id,year,month,myfactor. I tried this in MySQL but had no success so far.
Is there an easy way to do it in R? I though about adding another column to my data.frame and adding up conditions step by step… Maybe some %in% stuff ?

Thx in advance for suggestions…

Hmm, of course… here´s some example – sorry for not providing it immediately, my head hurts ;):

---

   myf   Year    month userid   
  1 A    2005       1    260           
  2 B    2005       2    260           
  3 B    2005       4    260           
  4 A    2005       5    260           
  5 B    2005       6    260           
  6 B    2005       1    261 

if this is my dataset, I want to update the changes column, counting the number of changes of myf per user. Basically id like to end up with:

  user  changes
   260     3
   260     0

and so forth…

HTH

Answer 1

#Some data
dfr <- data.frame(
   binary_variable = runif(100) < .7,
   id = sample(7, 100, replace = TRUE)
)

#Split by id
split_by_id <- with(dfr, split(binary_variable, id))

#Number of changes
sapply(split_by_id, function(x) sum(diff(x) != 0))