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cetnos
2003 Nov 14
2
bad performance of a function
...ll
I need to find a length of true sequences in logical vector (see example 1). I found
a possible solution which is good but if I use it on a larger data set I experience a
substantial decrease in performance (example 2).
Example 1
set.seed(111)
x <- sample(c(T,F),50, replace=T)
system.time(cetnost <- as.numeric(table(which(x)-cumsum(x[which(x)]))))
[1] 0.00 0.00 0.03 NA NA
cetnost
[1] 1 3 2 5 1 4 1 1 1 3 1 1 2
Example 2
x<-sample(c(T,F),40321*51, replace=T)
dd<-matrix(x,40321,51)
system.time(cetnost <- lapply(dd,function(x) as.numeric(table(which(x)-
cumsum(x[which(x)])))))...