r - Build summary table from matrix -

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i have matrix

mdat <- matrix(c(0,1,1,1,0,0,1,1,0,1,1,1,1,0,1,1,1,1,0,1), nrow = 4, ncol = 5, byrow = true)      [,1] [,2] [,3] [,4] [,5] [1,]    0    1    1    1    0 [2,]    0    1    1    0    1 [3,]    1    1    1    0    1 [4,]    1    1    1    0    1

and i'm trying build t:

     t1 t2 t3 row1  1  2  4 row2  2  2  3 row3  2  5  5 row4  3  1  3 row5  3  5  5 row6  4  1  3 row7  4  5  5

where each row in mdat: t1 shows mdat row number t2 shows mdat column there's first 1 t3 shows mdat column there's last consecutive 1.

therefore

row1 in t [1 2 4] because row 1 in mdat first 1 in column 2 , last consecutive 1 in column 4.

row2 in t [2 2 3] because row 2 in mdat first 1 in column 2 , last consecutive 1 in column 3.

this try:

for (i in 1:4){   (j in 1:5) {     if (mdat[i,j]==1) {t[i,1]<-i;t[i,2]<-j; cont<-0; while (mdat[i,j+cont]==1){     cont<-cont+1;     t[i,3]<-cont} } } }

here's strategy using apply/rle richard suggested.

xx<-apply(mdat, 1, function(x) {     r <- rle(x)     w <- which(r$values==1)     l <- r$lengths[w]     s <- cumsum(c(0,r$lengths))[w]+1     cbind(start=s,stop=s+l-1) }) do.call(rbind, map(cbind, row=seq_along(xx), xx))

we start finding runs of 1 on each row using "values" property of rle , calculate start , stop positions using "lengths" property. turn data list of 2 column matrices 1 list item per row of original matrix.

now use map add row number onto matrix , rbind results. seems give data you're after

     row start stop [1,]   1     2    4 [2,]   2     2    3 [3,]   2     5    5 [4,]   3     1    3 [5,]   3     5    5 [6,]   4     1    3 [7,]   4     5    5

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