# Finding max index in a vector

**URL:** <https://www.ruby-forum.com/t/finding-max-index-in-a-vector/240674>\
**Category:** GNU Radio\
**Created:** [April 25, 2014, 4:46am UTC](https://www.ruby-forum.com/t/finding-max-index-in-a-vector/240674 "2014-04-25T04:46:19Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [April 25, 2014, 4:46am UTC](https://www.ruby-forum.com/t/finding-max-index-in-a-vector/240674/1 "2014-04-25T04:46:19Z")

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How do I find the index of the max value in a vector from GRC?  
The max\_xx block outputs the max value, but not its  
index, despite what it’s documentation says:

“Data is passed in as a vector of length from multiple input sources.  
It will look through these streams of data items and output two  
streams. Stream 0 will contain the index value in the vector where the  
maximum value occurred.”

I checked the code template for max (GR v3.7.3), and it doesn’t even  
seem to retain the index of the max it reports.

@(^.^)@ Ed

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**Author:** ![Ed\_Criscuolo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ac8455/32.png) [@Ed\_Criscuolo](https://www.ruby-forum.com/u/Ed_Criscuolo)\
**Post date:** [April 25, 2014, 6:16pm UTC](https://www.ruby-forum.com/t/finding-max-index-in-a-vector/240674/2 "2014-04-25T18:16:19Z")

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On Thu, Apr 24, 2014 at 11:32 AM, Ed Criscuolo  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> I checked the code template for max (GR v3.7.3), and it doesn’t even  
> seem to retain the index of the max it reports.
> 
> @(^.^)@ Ed

Ed,

Yeah, this block does not match the description. It simply outputs the  
maximum value for a given vector of samples. I’m going to fix this now  
since I’m about to push a few other changes.

I can see a use for having the block have an optional secondary stream  
with  
the index value, though.

Tom

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**Author:** ![Ed\_Criscuolo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ac8455/32.png) [@Ed\_Criscuolo](https://www.ruby-forum.com/u/Ed_Criscuolo)\
**Post date:** [April 25, 2014, 6:16pm UTC](https://www.ruby-forum.com/t/finding-max-index-in-a-vector/240674/3 "2014-04-25T18:16:55Z")

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Hi Ed,  
I’m on a train. I wanted to try out how long it takes to do it  
including implementing rudimentary QA. So I just went ahead and tried:  
about 205s, most spent on figuring out how to get the IO signature  
straight.  
Enjoy: [Max index filter block · GitHub](https://gist.github.com/marcusmueller/11294819)

Greetings,  
Marcus

On 24.04.2014 17:32, Ed Criscuolo wrote:

> I checked the code template for max (GR v3.7.3), and it doesn’t  
> even seem to retain the index of the max it reports.
> 
> @(^.^)@ Ed
> 
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