[R] Running sum

[Liaw, Andy]

See cumsum:

> x <- rnorm(10)
> cs <- function(X) { 
+      N <- length(X)
+      Y <- vector(length=N)
+      Y[1] <- X[1]
+      for (i in 2:N) {
+        Y[i] <- Y[i-1]+X[i]
+      }
+      return(max(Y))
+ }
> cs(x)
[1] 3.228554
> max(cumsum(x))
[1] 3.228554

Andy

> From: Sean Davis
> 
> I have vector X of length N that I want to have a running sum for 
> (called Y).  I just need max(Y).  I do this with a "for" loop like so:
> 
>      Y <- vector(length=N)
>      Y[1] <- X[1]
>      for (i in 2:N) {
>        Y[i] <- Y[i-1]+X[i]
>      }
>      return(max(Y))
> 
> Is there a faster way to do this?
> 
> Thanks,
> Sean
> 
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