i working matrix containing large number of na. record length of each sequence of na in new matrix.
the following example should more plain.
#generating random 5x5 population matrix 15 na m=matrix(sample(1:9,25,t),5) m[sample(1:length(m),15,f)]=na dimnames(m)=list(paste(rep("city",dim(m)[1]),1:dim(m)[1],sep=""),paste(rep("year",dim(m)[2]),1:dim(m)[2],sep="")) m year1 year2 year3 year4 year5 city1 2 na na na na city2 na na na 6 8 city3 1 na na 6 na city4 na 5 na na 1 city5 8 na 1 na 2 the desired output following. e.g. 4 4 4 4 denotes sequence of 4 consecutive na.
year1 year2 year3 year4 year5 city1 0 4 4 4 4 city2 3 3 3 0 0 city3 0 2 2 0 1 city4 1 0 2 2 0 city5 0 1 0 1 0 do have idea of how go that?
not efficient code ever:
r1=c(1,1,na,1,1) r2=c(1,na,na,1,1) r3=c(1,na,na,na,1) r4=c(na,na,1,1,1) r5=c(1,1,1,na,na) m=rbind(r1,r2,r3,r4,r5) like @pascal pointed out, approach convert entire matrix characters, can assign 1s 0s instead , this:
m[m == 1] <- 0 (xx <- t(apply(m, 1, function(x) { s <- sum(is.na(x)) if (is.na(x[1])) x[is.na(x)] <- rep(4, s) else if (is.na(tail(x, 1))) x[is.na(x)] <- rep(5, s) else x[is.na(x)] <- s x }))) # [,1] [,2] [,3] [,4] [,5] # r1 0 0 1 0 0 # r2 0 2 2 0 0 # r3 0 3 3 3 0 # r4 4 4 0 0 0 # r5 0 0 0 5 5 this desired output. if don't believe me, convert 0s 1s , assign letters based on integers
xx[xx > 0] <- letters[xx[xx > 0]] xx[xx == '0'] <- 1 r1=c(1,1,"a",1,1) r2=c(1,"b","b",1,1) r3=c(1,"c","c","c",1) r4=c("d","d",1,1,1) r5=c(1,1,1,"e","e") r=rbind(r1,r2,r3,r4,r5) identical(r, xx) # [1] true 
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