# [R] "=" in functions and matlab (was: Multiplying each row of a big matrix with a vector)

From: Robin Hankin <r.hankin_at_noc.soton.ac.uk>
Date: Wed, 30 Jan 2008 08:56:47 +0000

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[this after a mistakenly private email to Megh]

As others have said, "%*%" is sufficiently vectorized to do what you want.

Speaking as a reformed Matlab user,
it might be as well to add that the definition of function fu() that you give looks like matlab code to me.

Check this out:

``` > f <- function(x){f = x^2}
> f(4)
>
> dput(f(4))
```

16
>

Thus fu() returns 16 but invisibly. This can be terribly confusing to those from a matlab background.

In R, one can just write

> f<- function(x){x^2}

because functions return the last evaluated expression.

Compare matlab, where(IIRC) one has to state in the function the name of the variable whose value will be returned.

HTH rksh

On 30 Jan 2008, at 07:20, Megh Dal wrote:

> I have a big matrix 'ret'. I want to multiply each row of it with a
> 2nd vector 'pos', resulting result, I want to save in a vector named
> 'port'. I wrote following code:
>
>> pos
> [1] 2593419 2130220 6198197 1673888 1980000 1784732 2052120
> -7490228 -5275000
>
>
>> dim(ret)
> [1] 500 9
>
>> fu # user defined function
> function(x)
> {
> fu = x %*% t(pos)
> }
> port = apply(ret, 1, fu)
>
>> dim(port)
> [1] 81 500
>
> My desire is to get port as a vector with length 500. However I am
> not getting that?
>
> Can anyone tell me how to correct that?
>
> Regards,
>
>
>
> ---------------------------------
>
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>
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```--
Robin Hankin
Uncertainty Analyst and Neutral Theorist,
National Oceanography Centre, Southampton
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tel  023-8059-7743

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