Including a vector element in an if statement

Hi all,

I've searched high and low on this and found nothing of help. I'm using
v2.6.2 and trying to write a function that will count how many people from a
dataset fall under a poverty line of 50% of the mean income.

a9 is my 100-element vector of incomes. I want pa9 to be my vector that
counts how many of these are classed as in poverty.

My problem is that my command if(a9[i] < mean(a9)/2 ) returns an "argument
is of length zero" error. But a9[i] is not really of length zero; if I
remove the if() command and simply set pa9[i] = a9[i] in the loop it comes
out fine.

I don't think it's a problem with the type of variable either, because if I
multiply the vector by 2 I get the "correct" output, so I think it's a
problem with R interpreting my vector as a list of strings or anything.

povertyline = function()
{
pa9 = c()
i=0
?while(i<=length(a9))
?{
? ?if(a9[i] < mean(a9)/2)
? ?{
? ?pa9[i] = a9[i]
? ?}
?i = i+1
?}
return(length(pa9))
}

Has anyone any ideas what's going wrong? (Just for clarification: yes, this
is for my homework. However I've already done the assignment in Excel and
I'm repeating it to improve my R'ing.)

Thanks a lot,
Enda

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