std::transform() in C++ STL (Perform an operation on all elements)

Consider the problem of adding contents of two arrays into a third array. It is given that all arrays are of same size.

Following is simple C++ program without transform().

// A C++ code to add two arrays
#include <bits/stdc++.h>
using namespace std;

int main()
{
  int arr1[] = {1, 2, 3};
  int arr2[] = {4, 5, 6};
  int n = sizeof(arr1)/sizeof(arr1[0]);
  int res[n];

  // Code to add two arrays
  for (int i=0; i<n; i++)
    res[i] = arr1[i] + arr2[i];

  for (int i=0; i<3; i++)
    cout << res[i] << " ";
}

Output :

5 7 9

Using transform function of STL, we can add arrays in single line.

// Using tansform() in STL to add two arrays
#include <bits/stdc++.h>
using namespace std;

int main()
{
  int arr1[] = {1, 2, 3};
  int arr2[] = {4, 5, 6};
  int n = sizeof(arr1)/sizeof(arr1[0]);
  int res[n];

  // Single line code to add arr1[] and arr2[] and
  // store result in res[]
  transform(arr1, arr1+n, arr2, res, plus<int>());

  for (int i=0; i<n; i++)
    cout << res[i] << " ";
}

Output :

5 7 9

transform() in C++ is used in two forms:

1. Unary Operation : Applies a unary operator on input to convert into output

   transform(Iterator inputBegin, Iterator inputEnd, 
            Iterator OutputBegin, unary_operation) 

   Following is C++ example.

   // C++ program to demonstrate working of
   // transform with unary operator.
   #include <bits/stdc++.h>
   using namespace std;
   
   int increment(int x) {  return (x+1); }
   
   int main()
   {
       int arr[] = {1, 2, 3, 4, 5};
       int n = sizeof(arr)/sizeof(arr[0]);
   
       // Apply increment to all elements of
       // arr[] and store the modified elements
       // back in arr[]
       transform(arr, arr+n, arr, increment);
   
       for (int i=0; i<n; i++)
           cout << arr[i] << " ";
   
       return 0;
   }

   Output :

   2 3 4 5 6 

2. Binary Operation : Applies a binary operator on input to convert into output

   transform(Iterator inputBegin1, Iterator inputEnd1, 
            Iterator inputBegin2, Iterator OutputBegin, 
            binary_operation) 

   The example mentioned above for adding two arrays is an example of transform with binary operation.

More examples:
We can use transform to convert a string to upper case (See this)

We can modify above examples for vectors also.

    
    // vect is a vector of integers.
    transform(vect.begin(), vect.end(), 
              vect.begin(), increment); 

Related Topic:
Functors in C++

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.