Decimate an array to a fixed length

[nitad54449]

Hello

I am plotting some data in 3D and is rather slow... so I am trying to decimate an array to a fixed length (I know the decimate function, it's not that simple) :

If I have an array of length N and want to decimate to an array of length M (both N and M are decided at runtime). I made something like this, I am wondering if you have a better way.

It's not that important, this thing works for me, but just wondering if there is a better way.

Thanks

[GerdW]

Hi nitad,

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@nitad54449 wrote:

I made something like this, I am wondering if you have a better way.

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• You only need to divide once before the loop.
• You can index the array elements inside your own loop so you don't need that additional green function with its own loop inside…

[nitad54449]

Hi

The divide in the loop is a rookie mistake,... but I don't get your second comment. I want to delete those indexes (or should I do it the other way around ? I mean I could use a conditional indexer, I was thinking this is slow). 

(well, slow, is maybe not that important but the "array in" has typically 2k to 10k length, each element is a cluster with 5 to 10 arrays of 100 to 500 doubles...)

thanks

[GerdW]

Hi nitad,

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@nitad54449 wrote:

I want to delete those indexes (or should I do it the other way around ? I mean I could use a conditional indexer, I was thinking this is slow). 

I don't use those green functions (OpenG? GPower?) so I cannot comment in their purpose just from looking at the image.

When I "decimate" an array I typically pick the elements that should remain instead of deleting all other elements - should be more performant when the decimation factor is >>1…

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@nitad54449 wrote:

the "array in" has typically 2k to 10k length, each element is a cluster with 5 to 10 arrays of 100 to 500 doubles...)

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Your "array in" is a 1D array of I32 values according to the image!? No clusters, no DBLs…

[nitad54449]

Hi

I put a simplified version, here is a real life vi

it takes 27 msec on my computer (the green stuff is openG)

[GerdW]

Hi nitad,

mind to share the VI downconverted to LV2019?

[nitad54449]

Hi

Here it is in 2019

A simpler version without OpenG (11 msec now), Vi attached.

[altenbach]

"Delete from array" should never be inside a tight loop! I'll have a look.

[GerdW · Accepted solution]

Hi nitad,

so you want to pick 200 elements out of ~3700 elements, so the solution is to delete ~3500 elements from the array?

I repeat: I would just pick the elements I need:

You may use a different rounding (or no rounding at all as ToI32 will also round)…

[nitad54449]

Hi

Nice, this Ramp stuff..

Now is in the msec range !

Thanks