Most of us have C++ as our First Language but when it comes to something like Data Analysis and Machine Learning, Python becomes our go-to Language because of its simplicity and plenty of libraries of pre-written Modules.
But can C++ be used for Machine Learning too? and If yes, then how?
Pre-requisites:
-
C++ Boost Library:- It is a powerful C++ library used for various purposes like big Maths Operations, etc.
You can refer here for installation of this Library -
ML pack C++ Library:- This is a small and Scalable C++ Machine Learning Library.
You can refer here for the installation of this Library.
Note: set USE_OPENMP=OFF when installing mlpack, don’t sweat, given link has guide on how to do that - Sample CSV Data File:- As MLpack library does not have any inbuilt Sample Dataset so we have to use our own Sample Dataset.
Our Model
The Code we are writing takes a simple dataset of vectors and finds the nearest neighbour for each data point.
The Training Part has been highlighted
Input : Our Input is a file named data.csv containing a dataset of vectors The File Contains the Following Data: 3, 3, 3, 3, 0 3, 4, 4, 3, 0 3, 4, 4, 3, 0 3, 3, 4, 3, 0 3, 6, 4, 3, 0 2, 4, 4, 3, 0 2, 4, 4, 1, 0 3, 3, 3, 2, 0 3, 4, 4, 2, 0 3, 4, 4, 2, 0 3, 3, 4, 2, 0 3, 6, 4, 2, 0 2, 4, 4, 2, 0
Code:
#include <mlpack/core.hpp> #include <mlpack/methods/neighbor_search/neighbor_search.hpp> using namespace std;
using namespace mlpack;
// NeighborSearch and NearestNeighborSort using namespace mlpack::neighbor;
// ManhattanDistance using namespace mlpack::metric;
void mlModel()
{ // Armadillo is a C++ linear algebra library;
// mlpack uses its matrix data type.
arma::mat data;
/*
data::Load is used to import data to the mlpack,
It takes 3 parameters,
1. Filename = Name of the File to be used
2. Matrix = Matrix to hold the Data in the File
3. fatal = true if you want it to throw an exception
if there is an issue
*/
data::Load( "data.csv" , data, true );
/*
Create a NeighborSearch model. The parameters of the
model are specified with templates:
1. Sorting method: "NearestNeighborSort" - This
class sorts by increasing distance.
2. Distance metric: "ManhattanDistance" - The
L1 distance, the sum of absolute distances.
3. Pass the reference dataset (the vectors to
be searched through) to the constructor.
*/
NeighborSearch<NearestNeighborSort, ManhattanDistance> nn(data);
// in the above line we trained our model or
// fitted the data to the model
// now we will predict
arma::Mat< size_t > neighbors; // Matrices to hold
arma::mat distances; // the results
/*
Find the nearest neighbors. Arguments are:-
1. k = 1, Specify the number of neighbors to find
2. Matrices to hold the result, in this case,
neighbors and distances
*/
nn.Search(1, neighbors, distances);
// in the above line we find the nearest neighbor
// Print out each neighbor and its distance.
for ( size_t i = 0; i < neighbors.n_elem; ++i)
{
std::cout << "Nearest neighbor of point " << i << " is point "
<< neighbors[i] << " and the distance is " << distances[i] << ".\n" ;
}
} int main()
{ mlModel();
return 0;
} |
Run the above code in Terminal/CMD using
g++ knn_example.cpp -o knn_example -std=c++11 -larmadillo -lmlpack -lboost_serialization
followed by
./knn_example
Output: Nearest neighbor of point 0 is point 7 and the distance is 1. Nearest neighbor of point 1 is point 2 and the distance is 0. Nearest neighbor of point 2 is point 1 and the distance is 0. Nearest neighbor of point 3 is point 10 and the distance is 1. Nearest neighbor of point 4 is point 11 and the distance is 1. Nearest neighbor of point 5 is point 12 and the distance is 1. Nearest neighbor of point 6 is point 12 and the distance is 1. Nearest neighbor of point 7 is point 10 and the distance is 1. Nearest neighbor of point 8 is point 9 and the distance is 0. Nearest neighbor of point 9 is point 8 and the distance is 0. Nearest neighbor of point 10 is point 9 and the distance is 1. Nearest neighbor of point 11 is point 4 and the distance is 1. Nearest neighbor of point 12 is point 9 and the distance is 1.
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