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Ramiro Diaz Trepat-2

Smalltalk idiom

I have a simple question regarding the use of a proper idiom.

I had to create a matrix (n X m) of random values and I used a line similar to this one:

NMatrix withRows: ((1 to: n) collect: [ :i | random next: m ]).

Since Smalltalk is so neat for its collection handling, I obviously did not like to write that line.

I thought that I did not want to explicitly create the interval, nor use a block that requires an

argument that I also don't use.

The question, finally, is if there an elegant way of replicating the behaviour of #collect: but

without the argument?

In my case, I thought it would be great for Integer to have something like #timesCollect:

that would allow me to rewrite the line above as:

NMatrix withRows: (n timesCollect: [ random next: m ])

Does anyone else think that this would be an useful method to have?

Cheers

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Igor Stasenko

Re: Smalltalk idiom

2009/5/20 Ramiro Diaz Trepat <[hidden email]>:
> I have a simple question regarding the use of a proper idiom.
> I had to create a matrix (n X m) of random values and I used a line similar
> to this one:
> NMatrix withRows: ((1 to: n) collect: [ :i | random next: m ]).

> Since Smalltalk is so neat for its collection handling, I obviously did not
> like to write that line.
> I thought that I did not want to explicitly create the interval, nor use a
> block that requires an
> argument that I also don't use.
> The question, finally, is if there an elegant way of replicating the
> behaviour of #collect: but
> without the argument?
> In my case, I thought it would be great for Integer to have something like
> #timesCollect:
> that would allow me to rewrite the line above as:
> NMatrix withRows: (n timesCollect: [ random next: m ])
> Does anyone else think that this would be an useful method to have?

depends on how you represent a matrix.
It seems that you using a collection of N rows.
IMO its more efficient to use a flat array, while you can declare the matrix as:

Array subclass: #NMatrix
instanceVariables: 'numRows'

then, an instance size \\ numRows - gives number of columns

and you can simply add/override some methods , while reuse most of
Collection protocol when you don't need to care about item row/col
position - like in regular flat Array.

Override a #species method, so NMatrix collect: will create NMatrix
when using #collect: and other related methods.
Then, a multiplication can be implemented as:

NMatrix >>* numberOrMatrix
^ numberOrMatrix isNumber ifTrue: [ self collect: [: each | each * number ] ]
ifFalse: [ self mulMatrix: numberOrMatrix ]

as you can see, a #collect: method can be used for scalar multiplication.

> Cheers
>
> r.
> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
>

--
Best regards,
Igor Stasenko AKA sig.

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ramiro.diaz.trepat

Re: Smalltalk idiom

Hi Igor,
Thank you very much for your thorough reply.
May be I did not express myself properly, but I am not really interested in discussing the implementation of a Matrix. It was only an example.
I'm interested in discussing wether or not people in the community find it neat and useful to have a method that behaves like #collect: but without arguments, just like #timesRepeat: for the iterations.
Sorry for the misunderstanding.
Cheers

r.

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Igor Stasenko
Sent: 20 May 2009 09:40
To: [hidden email]
Subject: Re: [Pharo-project] Smalltalk idiom

2009/5/20 Ramiro Diaz Trepat <[hidden email]>:
> I have a simple question regarding the use of a proper idiom.
> I had to create a matrix (n X m) of random values and I used a line similar
> to this one:
> NMatrix withRows: ((1 to: n) collect: [ :i | random next: m ]).