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How can find all peaks in float array?

I want to find peak in the float array,In this code I have get wrong output when there is a peak on an endpoint.How can I fix it?
// Util.cpp #include "Util.h" void diff(vector<float> in, vector<float>& out) { out = vector<float>(in.size()1); for(int i=1; i<(int)in.size(); ++i) out[i1] = in[i]  in[i1]; } void vectorProduct(vector<float> a, vector<float> b, vector<float>& out) { out = vector<float>(a.size()); for(int i=0; i<(int)a.size(); ++i) out[i] = a[i] * b[i]; } void findIndicesLessThan(vector<float> in, float threshold, vector<int>& indices) { for(int i=0; i<(int)in.size(); ++i) if(in[i]<threshold) indices.push_back(i+1); } void selectElements(vector<float> in, vector<int> indices, vector<float>& out) { for(int i=0; i<(int)indices.size(); ++i) out.push_back(in[indices[i]]); } void selectElements(vector<int> in, vector<int> indices, vector<int>& out) { for(int i=0; i<(int)indices.size(); ++i) out.push_back(in[indices[i]]); } void signVector(vector<float> in, vector<int>& out) { out = vector<int>(in.size()); for(int i=0; i<(int)in.size(); ++i) { if(in[i]>0) out[i]=1; else if(in[i]<0) out[i]=1; else out[i]=0; } } void Peaks::findPeaks(vector<float> x0, vector<int>& peakInds) { int minIdx = distance(x0.begin(), min_element(x0.begin(), x0.end())); int maxIdx = distance(x0.begin(), max_element(x0.begin(), x0.end())); float sel = (x0[maxIdx]x0[minIdx])/4.0; int len0 = x0.size(); vector<float> dx; diff(x0, dx); replace(dx.begin(), dx.end(), 0.0f, Peaks::EPS); vector<float> dx0(dx.begin(), dx.end()1); vector<float> dx1(dx.begin()+1, dx.end()); vector<float> dx2; vectorProduct(dx0, dx1, dx2); vector<int> ind; findIndicesLessThan(dx2, 0, ind); // Find where the derivative changes sign vector<float> x; vector<int> indAux(ind.begin(), ind.end()); selectElements(x0, indAux, x); x.insert(x.begin(), x0[0]); x.insert(x.end(), x0[x0.size()1]);; ind.insert(ind.begin(), 0); ind.insert(ind.end(), len0); int minMagIdx = distance(x.begin(), min_element(x.begin(), x.end())); float minMag = x[minMagIdx]; float leftMin = minMag; int len = x.size(); if(len>2) { float tempMag = minMag; bool foundPeak = false; int ii; // Deal with first point a little differently since tacked it on // Calculate the sign of the derivative since we tacked the first // point on it does not neccessarily alternate like the rest. vector<float> xSub0(x.begin(), x.begin()+3);//tener cuidado subvector vector<float> xDiff;//tener cuidado subvector diff(xSub0, xDiff); vector<int> signDx; signVector(xDiff, signDx); if (signDx[0] <= 0) // The first point is larger or equal to the second { if (signDx[0] == signDx[1]) // Want alternating signs { x.erase(x.begin()+1); ind.erase(ind.begin()+1); len = len1; } } else // First point is smaller than the second { if (signDx[0] == signDx[1]) // Want alternating signs { x.erase(x.begin()); ind.erase(ind.begin()); len = len1; } } if ( x[0] >= x[1] ) ii = 0; else ii = 1; float maxPeaks = ceil((float)len/2.0); vector<int> peakLoc(maxPeaks,0); vector<float> peakMag(maxPeaks,0.0); int cInd = 1; int tempLoc; while(ii < len) { ii = ii+1;//This is a peak //Reset peak finding if we had a peak and the next peak is bigger //than the last or the left min was small enough to reset. if(foundPeak) { tempMag = minMag; foundPeak = false; } //Found new peak that was lager than temp mag and selectivity larger //than the minimum to its left. if( x[ii1] > tempMag && x[ii1] > leftMin + sel ) { tempLoc = ii1; tempMag = x[ii1]; } //Make sure we don't iterate past the length of our vector if(ii == len) break; //We assign the last point differently out of the loop ii = ii+1; // Move onto the valley //Come down at least sel from peak if(!foundPeak && tempMag > sel + x[ii1]) { foundPeak = true; //We have found a peak leftMin = x[ii1]; peakLoc[cInd1] = tempLoc; // Add peak to index peakMag[cInd1] = tempMag; cInd = cInd+1; } else if(x[ii1] < leftMin) // New left minima leftMin = x[ii1]; } // Check end point if ( x[x.size()1] > tempMag && x[x.size()1] > leftMin + sel ) { peakLoc[cInd1] = len1; peakMag[cInd1] = x[x.size()1]; cInd = cInd + 1; } else if( !foundPeak && tempMag > minMag )// Check if we still need to add the last point { peakLoc[cInd1] = tempLoc; peakMag[cInd1] = tempMag; cInd = cInd + 1; } //Create output if( cInd > 0 ) { vector<int> peakLocTmp(peakLoc.begin(), peakLoc.begin()+cInd1); selectElements(ind, peakLocTmp, peakInds); //peakMags = vector<float>(peakLoc.begin(), peakLoc.begin()+cInd1); } } }
in test code I set a peak at end of array and the output is :
1.26083 0.975976 9.10844e44 //wrong number print
#include <iostream> #include "Util.h" using namespace std; int main() { float signal[14] = {1.22933,1.07635,1.23343,1.17653,1.2322,1.26083,0.371609,0.975976,0.539859,0.039658,0.039658,1.039658,0.949407,1.64061}; vector<float> in(signal, signal + sizeof(signal) / sizeof(float)); vector<int> out; Peaks::findPeaks(in, out); qDebug()<<"Maxima found:"; for(int i=0; i<out.size(); ++i) qDebug()<<in[out[i]]; }

Hi @zhmh,
at least for the diffing there is a std algorithm: https://en.cppreference.com/w/cpp/algorithm/adjacent_difference
Afterwards, you would just need to find the maxima, for which an algorigthm probably exists too, I'm just not aware of.
Regards

You could use std::max_element

@JHilk Then I'd say he should use a combination of both algorithms :)

@JHilk the std::max_element just find one peak I want to find all peaks in array

@zhmh than you should adjust the title of the topic :P
int main(int argc, char *argv[]) { QApplication a(argc, argv); std::srand(std::time(0)); std::vector<float> input; for(int i = 0; i < 100; i ++) input.push_back(rand()/static_cast<float>(RAND_MAX)); std::vector<float> output; std::copy_if(input.cbegin(), input.cend(), std::back_inserter(output),[threshold = 0.6](const auto value) >bool{ return value > threshold;}); qDebug() << output; // return a.exec(); }

If you define a peak as:
n is peak if abs(n1) < abs(n) and abs(n+1) < abs(n)That means the end points are special cases. So either add zero to beginning and end of your array or handle the special cases separately.

I guess you need to first make clear what you understand to be peaks. At first glance your code seems to be overly complicated. From a quick look you seem to use a mathematical definition for peaks as extremas of a continuous function defined by points where the first derivative is 0. Let's have a look at a few examples to help us understand what you define as peaks. Here is my understanding:
 (Positive) peaks: 1 2 3 4 5 4 3 2 1 > 5 is the peak in this sequence
 Negative peaks, i.e. valleys: 5 4 3 2 1 2 3 4 5 > Is 1 a peak in your definition?
 Plateaus (i.e. not peaks): 1 2 3 4 4 4 5 6 > None of the 4's is a peak because we go upwards after this again. Special case: 1 2 3 4 5 5 5 4 3 2 1 > I assume there should be a peak here, but which 5? Take the middle one? What if we have an even number of 5's in this example? Maybe you are talking about a real function definition for your sequence so that plateaus will not occur (if you have strongly monotonic functions).
 When are the first and last number in a sequence defined to be peaks? Without plateaus they are either always or never peaks. If you allow for plateaus this is a lot more complicated... Mathematically speaking the ends of your sequence (not considering plateaus) are always local extrema.
Number 1 is quite easy to check:
void Peaks::findPeaks(vector<float> x0, vector<int>& peakInds) { for(int i = 1; i < x0.size()1; ++i) { if(x0[i] > x0[i1] && x0[i] > x0[i+1]) peakInds.push_back(i); ... } }
If you want to include number 2, just add this line inside the loop:
if(x0[i] < x0[i1] && x0[i] < x0[i+1]) peakInds.push_back(i)
Plateaus would be a lot more complicated to detect. Let us know if you want to include those as well. And just as I said: you can either always or never include the first and last element.
BTW, there are two things about your code style I would change. First, there is no reason to put
findPeaks
into a class. If it is a namespace it would be okay, though. Second, with modern C++ there is no reason to use an outparameter to your function. Instead ofvoid Peaks::findPeaks(vector<float> x0, vector<int> &peakInds) { ... }
you should write:
vector<int> Peaks::findPeaks(const vector<float> &x0) { vector<int> peakInds; ... return peakInds; }
There are now things like returnvalueoptimization and copyellision which will make returning a vector as fast as using outparameters. Your approach only is advantageous when you want to add indices to an existing vector. Also note that I used
const vector<float> &x0
to avoid a copy of this vector. This is just good modern style...

this problem would make an cool interview exercise for someone expected to write waveform analysis software. LOL