| transfer the specific data in array A to array B [message #88245] |
Wed, 02 April 2014 11:37  |
lczhang123
Messages: 5
Registered: March 2014
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Junior Member |
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I got a question when I was trying to save the interested data from array A to a NEW array B.
j=0
FOR i=0,n-2 do begin
IF A[i+1]-A[i] gt 80 THEN BEGIN
B[j]=A[i]
j=j+1
ENDIF
ENDFOR
it seems theres something wrong with B[j]=A[i] should I define B as an array first? Or anyone has a better idea? I know it is a stupid question....sorry about that
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| Re: transfer the specific data in array A to array B [message #88247 is a reply to message #88245] |
Wed, 02 April 2014 11:51  |
Andy Sayer
Messages: 127
Registered: February 2009
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Senior Member |
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Yes, you have to define the array B before you can attempt to fill its elements like that.
There are other ways you could code something like the above, although if you're a beginner then try first however makes sense to you. :) For example, this should work:
ndata=n_elements(a)
for_b=where(a[1:ndata-2]-a[0:ndata-1] gt 80,nvals)
if nvals gt 0 then b=a[for_b]
And in case you need it, nvals in the above is the same as the final value of j.
Hope this helps,
Andy
On Wednesday, April 2, 2014 2:37:55 PM UTC-4, lczha...@gmail.com wrote:
> I got a question when I was trying to save the interested data from array A to a NEW array B.
>
>
>
> j=0
>
> FOR i=0,n-2 do begin
>
>
>
> IF A[i+1]-A[i] gt 80 THEN BEGIN
>
> B[j]=A[i]
>
> j=j+1
>
>
>
> ENDIF
>
>
>
> ENDFOR
>
>
>
> it seems theres something wrong with B[j]=A[i] should I define B as an array first? Or anyone has a better idea? I know it is a stupid question....sorry about that
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| Re: transfer the specific data in array A to array B [message #88248 is a reply to message #88247] |
Wed, 02 April 2014 11:52 |
Andy Sayer
Messages: 127
Registered: February 2009
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Senior Member |
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Ah, ninjad by Craig. :)
On Wednesday, April 2, 2014 2:51:00 PM UTC-4, AMS wrote:
> Yes, you have to define the array B before you can attempt to fill its elements like that.
>
>
>
> There are other ways you could code something like the above, although if you're a beginner then try first however makes sense to you. :) For example, this should work:
>
>
>
> ndata=n_elements(a)
>
>
>
> for_b=where(a[1:ndata-2]-a[0:ndata-1] gt 80,nvals)
>
>
>
> if nvals gt 0 then b=a[for_b]
>
>
>
> And in case you need it, nvals in the above is the same as the final value of j.
>
>
>
> Hope this helps,
>
>
>
> Andy
>
>
>
> On Wednesday, April 2, 2014 2:37:55 PM UTC-4, lczha...@gmail.com wrote:
>
>> I got a question when I was trying to save the interested data from array A to a NEW array B.
>
>>
>
>>
>
>>
>
>> j=0
>
>>
>
>> FOR i=0,n-2 do begin
>
>>
>
>>
>
>>
>
>> IF A[i+1]-A[i] gt 80 THEN BEGIN
>
>>
>
>> B[j]=A[i]
>
>>
>
>> j=j+1
>
>>
>
>>
>
>>
>
>> ENDIF
>
>>
>
>>
>
>>
>
>> ENDFOR
>
>>
>
>>
>
>>
>
>> it seems theres something wrong with B[j]=A[i] should I define B as an array first? Or anyone has a better idea? I know it is a stupid question....sorry about that
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| Re: transfer the specific data in array A to array B [message #88252 is a reply to message #88248] |
Wed, 02 April 2014 13:57 |
Andy Sayer
Messages: 127
Registered: February 2009
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Senior Member |
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To follow up a message the original poster sent via email, the question was asked about how to define 'b' beforehand when you don't know how big it is. The short answer is you can't really. What you could do is define 'b' to be the same size as 'a', and then shrink it afterwards when you know how many good elements there are. For example, this:
b=a
b[*] = !values.f_nan
And then after transferring valid values from a to b:
is_good=where(finite(b),ngood)
if ngood ct 0 then b=b[is_good]
Andy
On Wednesday, April 2, 2014 2:52:07 PM UTC-4, AMS wrote:
> Ah, ninjad by Craig. :)
>
>
>
> On Wednesday, April 2, 2014 2:51:00 PM UTC-4, AMS wrote:
>
>> Yes, you have to define the array B before you can attempt to fill its elements like that.
>
>>
>
>>
>
>>
>
>> There are other ways you could code something like the above, although if you're a beginner then try first however makes sense to you. :) For example, this should work:
>
>>
>
>>
>
>>
>
>> ndata=n_elements(a)
>
>>
>
>>
>
>>
>
>> for_b=where(a[1:ndata-2]-a[0:ndata-1] gt 80,nvals)
>
>>
>
>>
>
>>
>
>> if nvals gt 0 then b=a[for_b]
>
>>
>
>>
>
>>
>
>> And in case you need it, nvals in the above is the same as the final value of j.
>
>>
>
>>
>
>>
>
>> Hope this helps,
>
>>
>
>>
>
>>
>
>> Andy
>
>>
>
>>
>
>>
>
>> On Wednesday, April 2, 2014 2:37:55 PM UTC-4, lczha...@gmail.com wrote:
>
>>
>
>>> I got a question when I was trying to save the interested data from array A to a NEW array B.
>
>>
>
>>>
>
>>
>
>>>
>
>>
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>>>
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>>
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>>> j=0
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>>
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>>>
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>>> FOR i=0,n-2 do begin
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>>
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>>>
>
>>
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>>>
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>>
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>>>
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>>> IF A[i+1]-A[i] gt 80 THEN BEGIN
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>>
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>>>
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>>
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>>> B[j]=A[i]
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>>
>
>>>
>
>>
>
>>> j=j+1
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>>
>
>>>
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>>
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>>>
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>>>
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>>> ENDIF
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>>>
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>>>
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>>>
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>>> ENDFOR
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>>>
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>>>
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>>>
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>
>>> it seems theres something wrong with B[j]=A[i] should I define B as an array first? Or anyone has a better idea? I know it is a stupid question....sorry about that
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