
# Dear all,
# how to replace values in x by means in subgroups created in ...
# replace only these values where y=0 in continous sequence
# replace by mean calculated locally for each subgroup created by 
# continous sequence of 0,0,0 in parallel y vector, i.e. 
# where there is continous sequence of 0 in data frame vector y 
#    but we do not replace values in x[i], if y[i]!=0 
# we do not want use loops we do not use apply (not very fast) 


x      <-c(0 ,1,2,3,4,5,6,7,8,NA,NA,1  ,1 ,NA,2  ,2)
y      <-c(0 ,0,0,1,0,0,0,1,1,1 ,NA,0  ,0 ,0 ,0  ,1)
Must_be<-c(1 ,1,1,3,5,5,5,7,8,NA,NA,1.5,1 ,NA,1.5,2)

(df<-as.data.frame(cbind(x,y))  )

# I have traied many bad colusions based on cumsum, pmin, pmax, ... 
(mean_dfx_if_yIs0<-y*cumsum(x*y)/(cumsum(y)*y) )

# how to do this?
# thans for any advice 
# E

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