Summing the last n elements of a array

[ssmith490D]

I'm collecting data from an instrument once per minute and adding each value to an array. After many days there are alot of values in the array. I want to be able to select a time, ie 4 hours, and have the last 4 hours of values added together so it can be displayed. Any ideas. Thanks in advance for the help.

ssmith

[LabViewGuruWannabe · Accepted solution]

Use Array Subset and Add Array Elements.

Once per minute = 60 values per hour.

Number of Hours * 60 = number of elements you want.

So subtract Number of Elements from Array Size to get your index.

Quick and easy!

8-)

Message Edited by LabViewGuruWannabe on 12-26-2008 03:39 PM

Message Edited by LabViewGuruWannabe on 12-26-2008 03:40 PM

[tinnitus]

hello,

try this

Arg my pc is too slow 

Message Edité par tinnitus le 12-26-2008 03:40 PM

[smercurio_fc]

I'm guessing this is a continuation of this thread, so my suggestion below is based on this. In the screenshot you posted you are using Build Array. A couple of points first:

• Be aware that this operation will slow down your program over time, as you are continuously increasing the memory footprint by growing your array. 
• You do not need to use local variables to do that operation. Use a shift register that's attached to your outer while loop.

Now, as to your question: Since your samples are not evenly spaced, then you must determine where to take an array subset. To do this you need to know what the time was 4 hours ago, and determine which array element is beyond this. You can accomplish this by a simple comparison operator and then search the 1D array for the first True/False. This tells you where the 4-hour cutoff is, and where you can take the Array Subset.

[altenbach]

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tinnitus wrote:

try this

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From the other thread, it seems that ssmith is using LabVIEW 7.1. Attaching a 8.6 VI without any explanation is not very helpful.

[tinnitus]

hello altenbach,

there is a simple chain with simulated aquisition that a child could understand,

about 7.1.1 it 's written nowhere, on simple demand i can also repost or send a pict

good night ( at least for me)

@+

Tinnitus

[ssmith490D]

Thanks a lot. Works great.

ssmith