| Modifying an array while conserving memory [message #30878] |
Thu, 23 May 2002 17:12  |
Randall Skelton
Messages: 169
Registered: October 2000
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Senior Member |
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Hi all,
I have a large array and I would like to 'insert' some data into the
middle of it. Imagine an array of 1000 points and having 100 points to
insert beginning at index 500 (the resulting array will have 1100 points).
Typically, I do not know the length of data I wish to insert until after
'a' is defined.
a = findgen(1000)
b = randomu(seed,100)
c = fltarr(1100) ; seems wasteful to use more memory
c[0:499] = a[0:499]
c[500:599] = b
c[600:1099] = a[500:999]
In reality, 'a' is of order 2e7 so I would like to avoid making
multiple copies of it. Does anyone have any suggestions regarding the
most memory efficient way of doing this?
Many thanks,
Randall
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| Re: Modifying an array while conserving memory [message #30953 is a reply to message #30878] |
Fri, 24 May 2002 10:06  |
Xiangyun Qiu
Messages: 6
Registered: November 2001
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Junior Member |
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I was hoping this would only use memory size of about size(a) +
2*size(b) during
operation; when it's done, only size(a) + size(b). If the conccatination
causes the
problem, I currently have no solution to this.
Thanks,
Xiangyun
"Pavel A. Romashkin" wrote:
>
> I don't think this takes care of it. Temporary does not work like this.
> It is useful for modifying memory contents in place, but not for
> concatinating memory allocations together.
> Pavel
>
> Xiangyun Qiu wrote:
>>
>> Randall Skelton wrote:
>> Hi there,
>>
>> Provided TEMPORARY() function works as we expect, I think the following
>> steps can
>> use less memory:
>>
>> a = findgen(1000)
>> b = randomu(seed,100)
>> a = shift(TEMPORARY(a), 500)
>> c = [TEMPORARY(b),TEMPORARY(a)]
>> c = Shift(TEMPORARY(c), 500) ; here happens to be 500 too, because
>> 500 = 1000 - 500
>>
>> This solely rely on TEMPORARY function, live or die with it.
--
Xiangyun
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| Re: Modifying an array while conserving memory [message #30959 is a reply to message #30878] |
Fri, 24 May 2002 09:11 |
Pavel A. Romashkin
Messages: 531
Registered: November 2000
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Senior Member |
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I don't think this takes care of it. Temporary does not work like this.
It is useful for modifying memory contents in place, but not for
concatinating memory allocations together.
Pavel
Xiangyun Qiu wrote:
>
> Randall Skelton wrote:
> Hi there,
>
> Provided TEMPORARY() function works as we expect, I think the following
> steps can
> use less memory:
>
> a = findgen(1000)
> b = randomu(seed,100)
> a = shift(TEMPORARY(a), 500)
> c = [TEMPORARY(b),TEMPORARY(a)]
> c = Shift(TEMPORARY(c), 500) ; here happens to be 500 too, because
> 500 = 1000 - 500
>
> This solely rely on TEMPORARY function, live or die with it.
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| Re: Modifying an array while conserving memory [message #30962 is a reply to message #30878] |
Fri, 24 May 2002 08:43 |
Randall Skelton
Messages: 169
Registered: October 2000
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Senior Member |
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Well... after a few insightful words from a shy fellow at RSI, it seems
what I have been trying to do is absolutely impossible :(
Thanks to all who offered comments.
Randall
On Fri, 24 May 2002, Randall Skelton wrote:
> In for an inch, in for a mile... After reading the EDG it is now glaringly
> obvious why my naive 'realloc' attempt was doomed. It seems IDL provides
> access to the dymanic memory allocation routines as IDL_MemAlloc() and
> IDL_MemFree(). Of course, the one they forgot to write about is the
> function IDL_MemRealloc-- the symbols for which can be found in libidl.so.
>
> Cheers,
> Randall
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| Re: Modifying an array while conserving memory [message #30963 is a reply to message #30878] |
Fri, 24 May 2002 08:38 |
Xiangyun Qiu
Messages: 6
Registered: November 2001
|
Junior Member |
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Randall Skelton wrote:
Hi there,
Provided TEMPORARY() function works as we expect, I think the following
steps can
use less memory:
a = findgen(1000)
b = randomu(seed,100)
a = shift(TEMPORARY(a), 500)
c = [TEMPORARY(b),TEMPORARY(a)]
c = Shift(TEMPORARY(c), 500) ; here happens to be 500 too, because
500 = 1000 - 500
This solely rely on TEMPORARY function, live or die with it.
Xiangyun
>
> Hi all,
>
> I have a large array and I would like to 'insert' some data into the
> middle of it. Imagine an array of 1000 points and having 100 points to
> insert beginning at index 500 (the resulting array will have 1100 points).
> Typically, I do not know the length of data I wish to insert until after
> 'a' is defined.
>
> a = findgen(1000)
> b = randomu(seed,100)
> c = fltarr(1100) ; seems wasteful to use more memory
> c[0:499] = a[0:499]
> c[500:599] = b
> c[600:1099] = a[500:999]
>
> In reality, 'a' is of order 2e7 so I would like to avoid making
> multiple copies of it. Does anyone have any suggestions regarding the
> most memory efficient way of doing this?
>
> Many thanks,
> Randall
--
Xiangyun
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| Re: Modifying an array while conserving memory [message #30968 is a reply to message #30878] |
Fri, 24 May 2002 06:20 |
Randall Skelton
Messages: 169
Registered: October 2000
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Senior Member |
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In for an inch, in for a mile... After reading the EDG it is now glaringly
obvious why my naive 'realloc' attempt was doomed. It seems IDL provides
access to the dymanic memory allocation routines as IDL_MemAlloc() and
IDL_MemFree(). Of course, the one they forgot to write about is the
function IDL_MemRealloc-- the symbols for which can be found in libidl.so.
Cheers,
Randall
On Fri, 24 May 2002, Randall Skelton wrote:
> It seems this will be my 3rd feature request of the week as my long-shot
> attempts at using realloc on an IDL passed array have failed miserably :(
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