Hello,

I wrote this code which works fine on a single observation:

x<-100
y<-200
z<-125
aa<-150
if(x<z && y>z) {aa-z}
result: 25

I am trying to apply this logic where x,y,z,and aa are arrays but with very
little success.  I have tried using loops and whiles but I always get errors
of various types.  I have consulted a few manuals but with limited success.
My hopeful outcome would be:

data:
    X       Y      Z      AA
1 100  200    125     150
2 125   110    105    140
3 110    150   130    200
4 90    200     75    65

Here row 1 would return 25, row 2 would return nothing since Z<X, row 3
would be 50, row 4 would be nothing since X>Z.

In this case I am trying to return something where I could call the output a
variable "Z" which would become an array based on the logic above where the
members would be: (25, 50)

I tried using this where the variables are arrays:
if(x<z && y>z) {aa-z}
But I get "NULL"

 I tried using this where the variables are arrays:
if(x<z && y>z) {aa-z} else "NA"
But I get "NA"

When I tried using a loop:
for(i in 1:length(x)) if(x<z && y>z) {aa-z} else "NA"
I got "NULL"

An attempt at a "while" statement crashed.

The time series resource (
http://cran.r-project.org/doc/contrib/Ricci-refcard-ts.pdf) is way too
involved.  Most online sources I am finding are not good for "if" contingent
array manipulation.  Annoyingly, just saying aa-z will work across the
entire array but for some reason my ifs fail.  I know the R help group only
wants serious emails so hopefully this will indicate I gave it a
reasonable shot.

Please help

Thanks

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