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Re: Simple list question

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  Re: Simple list question Bill Rowe <readnews@sbcglobal.net> - 2014-04-15 03:02 +0000
    Speed of Join and Append.   Was Re: Simple list question Richard Fateman <fateman@cs.berkeley.edu> - 2014-04-16 07:40 +0000

#16810 — Re: Simple list question

On 4/14/14 at 5:28 AM, stevebg@roadrunner.com (Ste[hen Gray) wrote:

>pcin = 2;
>pcex = 3;   (*pcin and pcex can have various small values *)
>
>coin = Table[{10 RandomReal[], 10 RandomReal[]}, {pcin}]
>coex = Table[{3 RandomReal[], 3 RandomReal[]}, {pcex}]
>cobo = Append[coin, coex]
>pcin = 2;
>pcex = 3;   (*pcin and pcex can have various small values *)
>
>coin = Table[{10 RandomReal[], 10 RandomReal[]}, {pcin}]
>coex = Table[{3 RandomReal[], 3 RandomReal[]}, {pcex}]
>cobo = Append[coin, coex]

<snip>

>What I want is a series of x,y coordinates with no extra nesting:

Instead of Append, use Join, i.e.

cobo = Join[coin, coex]

In fact, Append is something to generally avoid using
particularly for large arrays due to the computing resources
used. It will require more memory and is slower. Won't matter
for small arrays like this. But for large arrays, Append is very
much a problem and better replaced with other commands such as Join.

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#16813 — Speed of Join and Append. Was Re: Simple list question

On 4/14/2014 8:02 PM, Bill Rowe wrote:
> On 4/14/14 at 5:28 AM, stevebg@roadrunner.com (Ste[hen Gray) wrote:
>
>> pcin = 2;
>> pcex = 3;   (*pcin and pcex can have various small values *)
>>
>> coin = Table[{10 RandomReal[], 10 RandomReal[]}, {pcin}]
>> coex = Table[{3 RandomReal[], 3 RandomReal[]}, {pcex}]
>> cobo = Append[coin, coex]
>> pcin = 2;
>> pcex = 3;   (*pcin and pcex can have various small values *)
>>
>> coin = Table[{10 RandomReal[], 10 RandomReal[]}, {pcin}]
>> coex = Table[{3 RandomReal[], 3 RandomReal[]}, {pcex}]
>> cobo = Append[coin, coex]
>
> <snip>
>
>> What I want is a series of x,y coordinates with no extra nesting:
>
> Instead of Append, use Join, i.e.
>
> cobo = Join[coin, coex]
>
> In fact, Append is something to generally avoid using
> particularly for large arrays due to the computing resources
> used. It will require more memory and is slower. Won't matter
> for small arrays like this. But for large arrays, Append is very
> much a problem and better replaced with other commands such as Join.
>
>

You are, I think, confusing the conventional implementation of lists,
append and cons from Lisp, and the peculiar implementation in 
Mathematica of Append and Join.

I expect that in Mathematica they are equally wasteful, because
lists are represented by arrays and must be copied whether to
join or append.

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