Cross Concatenate Elements of 2 Vectors to Produce a Third

Question

I have 2 vectors and want to distribute one across the other to form a third vector like:

V1 = (a,b,c)
V2 = (d,e,f)

Result:

V3 = (ad,ae,af,bd,be,bf,...cf) 'nine total elements

The only way I know how to do it is by looping. I've tried searching a number of different ways, and can't find a 'one line of code' solution, to avoid looping.

If I've missed it, please point me to it. I may have not found the right search parameters.

If it is not possible, please spare me my misery and let me know :,,,(.

If there is an answer, please share it.

Answer 1

You do not make clear what operation ab means. I'll assume here you want to multiply two real numbers.

In Python, you can use a comprehension. Here a complete code snippet.

v1 = (2, 3, 5)
v2 = (7, 11, 13)
v3 = tuple(x * y for x in v1 for y in v2)

The value for v3 is then

(14, 22, 26, 21, 33, 39, 35, 55, 65)

as wanted. If you want a Python list, the code looks easier: use

v3 = [x * y for x in v1 for y in v2]

It will be obvious how to change the operation to concatenation or anything else desired. Here is sample code for concatenation of strings:

v1 = ('a', 'b', 'c')
v2 = ('d', 'e', 'f')
v3 = tuple(x + y for x in v1 for y in v2)

which results in

('ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf')

You could also use product() from the itertools module (which I used in the first version of this answer) but the above seems easier.

Answer 2

In R:
as.vector(sapply(V1, function(x) paste0(x, V2)))

Answer 3

In C++:

std::vector<decltype(v1.front() * v2.front())> v3 { v1[0] * v2[0], v1[0] * v2[1], v1[0] * v2[2], v1[1] * v2[0], v1[1] * v2[1], v1[1] * v2[2], v1[2] * v2[0], v1[2] * v2[1], v1[2] * v2[2] };

...though, I usually would format it in multiple lines.

As MCVE:

#include <iostream>
#include <vector>
using namespace std;

template <typename ELEM>
ostream& operator << (ostream &out, const vector<ELEM> &vec)
{
  const char *sep = "{ ";
  for (const ELEM &elem : vec) { out << sep << elem; sep = ", "; }
  return out << " }";
}

int main()
{
  vector<double> v1{ 1.0, 2.0, 3.0 }, v2{ 4.0, 5.0, 6.0 };
  // in one line:
  vector<decltype(v1.front() * v2.front())> v3 { v1[0] * v2[0], v1[0] * v2[1], v1[0] * v2[2], v1[1] * v2[0], v1[1] * v2[1], v1[1] * v2[2], v1[2] * v2[0], v1[2] * v2[1], v1[2] * v2[2] };
  // output:
  cout << v3 << endl;
  // done
  return 0;
}

Output:

{ 4, 5, 6, 8, 10, 12, 12, 15, 18 }

(Tested on ideone.)

Thanks, Rory Daulton, for the inspiration. In C++, I can do this also:

#include <iostream>
#include <string>
#include <vector>

using namespace std;

string operator*(const string &str1, const string &str2)
{
  return str1 + str2;
}

template <typename ELEM>
ostream& operator << (ostream &out, const vector<ELEM> &vec)
{
  const char *sep = "{ ";
  for (const ELEM &elem : vec) { out << sep << elem; sep = ", "; }
  return out << " }";
}

int main()
{
  vector<string> v1{ "a", "b", "c" }, v2{ "d", "e", "f" };
  // in one line:
  vector<decltype(v1.front() * v2.front())> v3 { v1[0] * v2[0], v1[0] * v2[1], v1[0] * v2[2], v1[1] * v2[0], v1[1] * v2[1], v1[1] * v2[2], v1[2] * v2[0], v1[2] * v2[1], v1[2] * v2[2] };
  // output:
  cout << v3 << endl;
  // done
  return 0;
}

Output:

{ ad, ae, af, bd, be, bf, cd, ce, cf }

After a little improvement, it will even work for mixed types:

#include <iostream>
#include <string>
#include <vector>

using namespace std;

string operator*(const string &arg1, int arg2)
{
  string ret; for (int i = 0; i < arg2; ++i) ret += arg1;
  return ret;
}

template <typename ELEM>
ostream& operator << (ostream &out, const vector<ELEM> &vec)
{
  const char *sep = "{ ";
  for (const ELEM &elem : vec) { out << sep << elem; sep = ", "; }
  return out << " }";
}

int main()
{
  vector<string> v1{ "a", "b", "c" }; vector<int> v2{ 1, 2, 3 };
  // in one line:
  vector<decltype(v1.front() * v2.front())> v3 { v1[0] * v2[0], v1[0] * v2[1], v1[0] * v2[2], v1[1] * v2[0], v1[1] * v2[1], v1[1] * v2[2], v1[2] * v2[0], v1[2] * v2[1], v1[2] * v2[2] };
  // output:
  cout << v3 << endl;
  // done
  return 0;
}

Output:

{ a, aa, aaa, b, bb, bbb, c, cc, ccc }