Given a matrix of MxN
  want to take the means of rows in the following fashion
m<-matrix(seq(1,80),ncol=20, nrow=4)
 result<-matrix(NA,nrow=4,ncol=20/5)
 result[,1]<-apply(m[,1:5],1,mean)
 result[,2]<-apply(m[,6:10],1,mean)
 result[,3]<-apply(m[,11:15],1,mean)
 result[,4]<-apply(m[,16:20],1,mean)
 result
     [,1] [,2] [,3] [,4]
[1,]    9   29   49   69
[2,]   10   30   50   70
[3,]   11   31   51   71
[4,]   12   32   52   72

So, I want the mean of every successive 5 values in a row

as the dimension in columns is wide I cant write it with multiple apply as
above

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