Question

I am facing a challenge and wanted to ask for your suggestions.

I am coding in c/c++ and I have an array like below.

A[40]={0,0,1,0,2,7,18,45,80,85,88,91,88,65,12,3,0,1,0,2,1,2,5,45,88,89,78,79,65,12,5,2,1,0,0,1,0,0,1}

As you can see, there are 2 rises that we can also call them curves.
This array stores the value of a real-time signal respect to the time.It works like a queue and refresh itself for every new value.

I want to detect and count the rises, I’ve tried some methods so far but couldn’t figure out a consistent solution yet.

My question is: how can I detect these curves and tell that there are 2 curves in array A?

Do you know any good way to detect them coherently? Or is there a method or something to handle this kind of signal works?

I really need the answer to advance on my project so all your answers are welcome. Thanks in advance.

Answer 1

You can spot peaks in your data by looking for the points where the sign flips when comparing neighbouring values:

#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>

namespace {
  int diff(const int& a, const int& b) {
    if (b-a > 0) 
      return 1;
    else if (b-a < 0) 
      return -1;
    return 0;
  }
}

int main() {
  const int A[]={0,0,1,0,2,7,18,45,80,85,88,91,88,65,12,3,0,1,0,2,1,2,5,45,88,89,78,79,65,12,5,2,1,0,0,1,0,0,1};
  std::vector<int> delta;
  std::transform(A, A+((sizeof A/sizeof *A) - 1), A+1, std::back_inserter(delta), diff);
  for (std::vector<int>::const_iterator it = ++delta.begin(); it != delta.end(); ++it) {
    if (*it < 0 && *it != *(it - 1))
      std::cout << "Peak at: " << A[it-delta.begin()] << "\n";
  }
}

Note that you actually have more than two peaks in your data:

Peak at: 1
Peak at: 91
Peak at: 1
Peak at: 2
Peak at: 89
Peak at: 79
Peak at: 1

If they’re not really peaks (just noise in the data) then you could fix that in a few of ways:

1. Quantization of the data.
2. Smoothing – i.e. alter each value to be more like its neighbours in some way.
3. Threshold. Record not just the sign, but the magnitude. Ignore changes smaller than a certain size.