[R] for loop problem

[Tobias Verbeke]

Dear list,

Here's a function that works fine
when I assign one value to i.
qx, ax and gr are vectors.
 
ax.to.nax <- function(qx, ax, gr=c(0,1,5,10)){
px <- 1 - qx
last.n <- gr[length(gr)] - gr[length(gr) - 1]
all.bounds <- c(gr, gr[length(gr)] + last.n)
n <- diff(all.bounds)
#
i <- 1 # this i should loop through the values of
       # gr: i=0, i=1, i=5 and i=10.
#
testprod <- prod(px[(i+1):(i+n[i+1])])
return(1 - testprod)
}

Every attempt to loop through
the values of gr, gives the following
error message:

Error in (i + 1):(i + n[i + 1]) : NA/NaN argument


Here is an example of the deplorably 
erroneous code that causes the message
to appear:

ax.to.nax.for <- function(qx, ax, gr=c(0,1,5,10)){
px <- 1 - qx
last.n <- gr[length(gr)] - gr[length(gr) - 1]
all.bounds <- c(gr, gr[length(gr)] + last.n)
n <- diff(all.bounds)
testprod <- numeric(length(gr))
for (j in 1:length(gr)){
  i <- gr[j]
  testprod[j] <- prod(px[(i+1):(i+n[i+1])])
  }
return(1 - testprod)
}


In what way am I ill-treating R ?



Thanks in advance,

Tobias