Although I think I understand "every 10 numbers", I am not so sure how to 
interpret "subtract aa from AA" for a couple of reasons.

First, to decimate your data:
ab <- AA[(1:10)*10]

As for subtraction, you have not told us what variable aa is. If you meant 
variable ab, it has only 10 values while AA has 100 values. If you try to 
subtract ab, R will "recycle" values until you get 10 copies of ab.

If you are thinking of set difference, there is a setdiff function, but that 
will only work reliably with integer data (which you have here but may not in 
general). However, you may find reading the section on indexing in the 
Introduction to R document that ships with R to be very useful. In there it 
mentions the effect of using negative index values:

AA[-(1:10)*10]

giving you "the rest of the data".
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Jie Tang <totang...@gmail.com> wrote:

>hi R users
>  I have a data set with the name AA
>AA<-1:100
>Now I want to get a child array from AA every 10 numbers
>e.g.
>ab =c(10,20,30,40,50,60,70,80,100)
>
>How could I subtract aa from AA?
>thank you .

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