Comparing elements of array with previous ones and insert index of elements where v[i+1]<v[i] in another array

[ptavernise2345]

Hi,

i'm new to Labview. I'd like to get some helps to solve this kind of problem. I've got an array of integer in input and i must compare every element with previous one. If the element in i-th position is less than previous(i-1 th) then i must insert index of this element in another array in output, else if the element in i-th position is greather than previous(i-1 th) then i must insert zero in output array.

Example

Array in input=[1,36,2,3,43,6,8,1]

Array in output=[0,2,0,0,5,0,7]

Any helps would be kindly appreciated. Thank you so much.

[udka]

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[GerdW · Accepted solution]

Hi ptavernise,

you need a FOR loop with a shift register.

By autoindexing through your input array you can compare the current element with the previous one you have stored in the shift register.

Connect the result of the comparison to a Select node and output either zero or the loop ietration count…

This is very basic LabVIEW stuff - you surely have seen the Getting Started section in the header of the LabVIEW board…

Spoiler

A different solution than the one described above:

[ptavernise2345]

This is the VI. I don't know why it doesn't work?

[GerdW · Accepted solution]

Hi ptavernise,

you don't compare with previous value. Instead you compare with the previous result (zero or index)…

Additionally you shouldn't wire a constant to "N" when you want to employ autoindexing.

And you should create an array output (using autoindexing again) to create your "array 2"!

Why did you mark your own question with a erranous VI as solution?

[ptavernise2345]

Hi,

i'm new to labview.I have a signal with its samples in an array and i like to find local maxima and minima, report it on the waveform and detect values of local maxima and minima. For example if we have i, i+1, i+2, i+3, i+4 we can define local maxima v[i+2] if v[i+2]>v[i],v[i+2]>v[i+1],v[i+2]>v[i+3],v[i+2]>v[i+4]. If we have i, i+1, i+2, i+3, i+4 we can define local minima v[i+2] if v[i+2]<v[i],v[i+2]<v[i+1],v[i+2]<v[i+3],v[i+2]<v[i+4].

How can i do?

Thank you so much

any help would be kindly appreciated

[GerdW]

Hi ptavernise,

so you already got solutions to find elements with x[i]<x[i-1], but you struggle to find elements with x[i]>x[i-1]?

Please stick with your threads as long the topic doesn't change!

[ptavernise2345]

I know the definition but i don't know how to implement vi.This is the main problem.

[GerdW]

Hi ptavernise,

you really should learn how to use shift registers…

[ptavernise2345]

This is the VI i have created. I cannot understand where is the error.Please help me, i really appreciate your help.

Thank you so much for helping me.