C++/STL Algorithms Modifying sequence operations/transform — различия между версиями
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Версия 14:21, 25 мая 2010
Содержание
- 1 Compute the difference
- 2 Create a sequence that contains the midpoints between the values in two other sequences.
- 3 Demonstrate both unary and binary function objects.
- 4 demonstrate the two-sequence form of transform()
- 5 std::transform with predicate
- 6 Subtract the mean from every data point
- 7 Transform all elements into deque from set by multiplying 10
- 8 Use a binary function object to find the midpoints between elements in v3 and v4 and store the results in v5.
- 9 Use generic template function with transform
- 10 Use transform function to square all elements in an array
- 11 Use transform to add each element traversed forward with each element traversed backward
- 12 Use transform to make the numbers in a list go from a certain range
- 13 Use transform to negate all elements in a container
- 14 Use transform to print differences of two corresponding elements
- 15 Use transform to print elements negatively and in reverse order
- 16 Use transform to square each element
- 17 Use transform to transform elements in one container into another container with ten times their value
Compute the difference
#include <algorithm>
#include <functional>
#include <iomanip>
#include <vector>
#include <iostream>
using namespace std;
template <class T>
void print(T& c){
for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
std::cout << *i << endl;
}
}
int main()
{
const float d1[] = { 1.11, 2.22, 3.33, 4.44, 5.55 };
const float d2[] = { 6.66, 7.77, 8.88, 9.99, 1.11 };
vector<float> v2( d2,d2 + sizeof( d2 ) / sizeof( d2[0] ) );
vector<float> v1( d1,d1 + sizeof( d1 ) / sizeof( d1[0] ) );
vector<float> change( v2.size() );
transform( v2.begin(), v2.end(), v1.begin(),change.begin(), minus<float>() );
print( change );
}
Create a sequence that contains the midpoints between the values in two other sequences.
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
double reciprocal(double val);
template<class T> void show(const char *msg, vector<T> vect);
int main(){
int i;
vector<double> v;
for(i=1; i < 10; ++i)
v.push_back((double)i);
show("Initial contents of v:", v);
cout << endl;
vector<double> v2(10);
transform(v.begin(), v.end(), v2.begin(), reciprocal);
show("v2:", v2);
return 0;
}
template<class T> void show(const char *msg, vector<T> vect) {
cout << msg << endl;
for(unsigned i=0; i < vect.size(); ++i)
cout << vect[i] << endl;
}
// Return the reciprocal
double reciprocal(double val) {
if(val == 0.0)
return 0.0;
return 1.0 / val;
}
Demonstrate both unary and binary function objects.
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
using namespace std;
// A function object that computes a reciprocal.
class reciprocal : unary_function<double, double> {
public:
result_type sum;
result_type operator()(argument_type val) {
if(val == 0.0)
return 0.0;
return 1.0 / val; // return reciprocal
}
};
int main(){
int i;
vector<double> v;
for(i=1; i < 10; ++i) v.push_back((double)i);
transform(v.begin(), v.end(), v.begin(), reciprocal());
return 0;
}
demonstrate the two-sequence form of transform()
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int midpoint(int a, int b);
template<class T> void show(const char *msg, vector<T> vect);
int main()
{
int i;
vector<double> v;
for(i=1; i < 10; ++i)
v.push_back((double)i);
show("Initial contents of v:", v);
vector<int> v3, v4, v5(10);
for(i = 0; i < 10; ++i)
v3.push_back(i);
for(i = 10; i < 20; ++i) {
if(i%2) {
v4.push_back(i);
}else {
v4.push_back(-i);
}
}
show("Contents of v3:", v3);
show("Contents of v4:", v4);
transform(v3.begin(), v3.end(), v4.begin(), v5.begin(), midpoint);
show("Contents of v5:", v5);
return 0;
}
template<class T> void show(const char *msg, vector<T> vect) {
cout << msg << endl;
for(unsigned i=0; i < vect.size(); ++i)
cout << vect[i] << endl;
}
// Return the whole-number midpoint between two values.
int midpoint(int a, int b) {
return((a-b) / 2) + b;
}
std::transform with predicate
#include <iostream>
using std::cout;
using std::endl;
#include <algorithm>
#include <numeric>
#include <vector>
#include <iterator>
int calculateCube( int );
int main()
{
std::ostream_iterator< int > output( cout, " " );
int a2[ 10 ] = { 100, 2, 8, 1, 50, 3, 8, 8, 9, 10 };
std::vector< int > v2( a2, a2 + 10 ); // copy of a2
cout << "Vector v2 contains: ";
std::copy( v2.begin(), v2.end(), output );
std::vector< int > cubes( 10 ); // instantiate vector cubes
// calculate cube of each element in v; place results in cubes
std::transform( v2.begin(), v2.end(), cubes.begin(), calculateCube );
cout << "\n\nThe cube of every integer in Vector v is:\n";
std::copy( cubes.begin(), cubes.end(), output );
cout << endl;
return 0;
}
int calculateCube( int value )
{
return value * value * value;
}
/*
Vector v2 contains: 100 2 8 1 50 3 8 8 9 10
The cube of every integer in Vector v is:
1000000 8 512 1 125000 27 512 512 729 1000
*/
Subtract the mean from every data point
#include <algorithm>
#include <cmath>
#include <functional>
#include <iostream>
#include <list>
#include <numeric>
#include <vector>
using namespace std;
template <class T>
void print(T& c){
for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
std::cout << *i << endl;
}
}
int main(){
const float a[] = { 1, 1.3, 1.5, 0.9, 0.1, 0.2};
vector<float> data( a,a + sizeof( a ) / sizeof( a[0] ) );
cout << data.size() << " ELEMENTS\n";
print( data );
// compute the mean
float mean = accumulate( data.begin(), data.end(), 0.0f )/ data.size();
// subtract the mean from every data point
vector<float> zero_mean( data );
transform( zero_mean.begin(), zero_mean.end(), zero_mean.begin(),bind2nd( minus<float>(), mean ) );
print( zero_mean );
}
Transform all elements into deque from set by multiplying 10
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <set>
#include <deque>
#include <algorithm>
using namespace std;
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
int main()
{
set<int,greater<int> > coll1;
deque<int> coll2;
// insert elements from 1 to 9
for (int i=1; i<=9; ++i) {
coll1.insert(i);
}
PRINT_ELEMENTS(coll1,"initialized: ");
// transform all elements into coll2 by multiplying 10
transform (coll1.begin(),coll1.end(), // source
back_inserter(coll2), // destination
bind2nd(multiplies<int>(),10)); // operation
PRINT_ELEMENTS(coll2,"transformed: ");
}
/*
initialized: 9 8 7 6 5 4 3 2 1
transformed: 90 80 70 60 50 40 30 20 10
*/
Use a binary function object to find the midpoints between elements in v3 and v4 and store the results in v5.
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
using namespace std;
// finds the midpoint between two values.
class midpoint : binary_function<int, int, double> {
public:
result_type operator()(first_argument_type a, second_argument_type b) {
return((a-b) / 2) + b;
}
};
int main(){
int i;
vector<int> v3, v4, v5(10);
for(i = 0; i < 10; ++i)
v3.push_back(i);
for(i = 10; i < 20; ++i)
if(i%2)
v4.push_back(i);
else
v4.push_back(-i);
transform(v3.begin(), v3.end(), v4.begin(), v5.begin(), midpoint());
return 0;
}
Use generic template function with transform
/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
using namespace std;
template <typename T, int VAL>
T addValue (T const& x)
{
return x + VAL;
}
void call_addValue()
{
addValue<int,5>(42);
}
template <typename IT, typename OP>
void transform (IT beg, IT end, IT to, OP op)
{
while (beg != end) {
*to++ = op(*beg++);
}
}
int main()
{
call_addValue();
int m[] = { 1, 2, 3, 4, 5, 6 };
transform (m, m+6,
m,
(int(*)(int const&)) // cast necessary
addValue<int,5>);
for(int i=0;i<6;i++){
cout << m[i] << " ";
}
}
/*
6 7 8 9 10 11
*/
Use transform function to square all elements in an array
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <algorithm>
#include <functional>
#include <iterator>
using namespace std;
int main()
{
int coll[] = { 5, 6, 2, 4, 1, 3 };
// square all elements
transform (coll, coll+6, // first source
coll, // second source
coll, // destination
multiplies<int>()); // operation
// print all elements
copy (coll, coll+6,
ostream_iterator<int>(cout," "));
cout << endl;
}
/*
25 36 4 16 1 9
*/
Use transform to add each element traversed forward with each element traversed backward
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll1;
list<int> coll2;
INSERT_ELEMENTS(coll1,1,9);
PRINT_ELEMENTS(coll1,"coll1: ");
/* add each element traversed forward with each element traversed backward
* and insert result into coll2
*/
transform (coll1.begin(), coll1.end(), // first source range
coll1.rbegin(), // second source range
back_inserter(coll2), // destination range
plus<int>()); // operation
PRINT_ELEMENTS(coll2,"coll2: ");
}
/*
coll1: 1 2 3 4 5 6 7 8 9
coll2: 10 10 10 10 10 10 10 10 10
*/
Use transform to make the numbers in a list go from a certain range
#include <algorithm>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <list>
using namespace std;
int main( )
{
list<int> data( 100000 );
// create random numbers
generate( data.begin(), data.end(), rand );
// make them go from 0 to 200
transform( data.begin(), data.end(), data.begin(),bind2nd( modulus<int>(), 201 ) );
// make them go from -100 to 100
transform( data.begin(), data.end(), data.begin(),bind2nd( minus<int>(), 100 ) );
}
Use transform to negate all elements in a container
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll1;
list<int> coll2;
INSERT_ELEMENTS(coll1,1,9);
PRINT_ELEMENTS(coll1,"coll1: ");
// negate all elements in coll1
transform (coll1.begin(), coll1.end(), // source range
coll1.begin(), // destination range
negate<int>()); // operation
PRINT_ELEMENTS(coll1,"negated: ");
}
/*
coll1: 1 2 3 4 5 6 7 8 9
negated: -1 -2 -3 -4 -5 -6 -7 -8 -9
*/
Use transform to print differences of two corresponding elements
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll1;
list<int> coll2;
INSERT_ELEMENTS(coll1,1,9);
PRINT_ELEMENTS(coll1,"coll1: ");
// print differences of two corresponding elements
cout << "diff: ";
transform (coll1.begin(), coll1.end(), // first source range
coll2.begin(), // second source range
ostream_iterator<int>(cout, " "), // destination range
minus<int>()); // operation
cout << endl;
}
/*
coll1: 1 2 3 4 5 6 7 8 9
diff: 2 3 4 5 6 7 8 9 10
*/
Use transform to print elements negatively and in reverse order
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll1;
list<int> coll2;
INSERT_ELEMENTS(coll1,1,9);
PRINT_ELEMENTS(coll1,"coll1: ");
// print coll2 negatively and in reverse order
transform (coll2.rbegin(), coll2.rend(), // source range
ostream_iterator<int>(cout," "), // destination range
negate<int>()); // operation
cout << endl;
}
/*
coll1: 1 2 3 4 5 6 7 8 9
*/
Use transform to square each element
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll1;
list<int> coll2;
INSERT_ELEMENTS(coll1,1,9);
PRINT_ELEMENTS(coll1,"coll1: ");
// square each element
transform (coll1.begin(), coll1.end(), // first source range
coll1.begin(), // second source range
coll1.begin(), // destination range
multiplies<int>()); // operation
PRINT_ELEMENTS(coll1,"squared: ");
}
/*
coll1: 1 2 3 4 5 6 7 8 9
squared: 1 4 9 16 25 36 49 64 81
*/
Use transform to transform elements in one container into another container with ten times their value
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
vector<int> coll1;
list<int> coll2;
INSERT_ELEMENTS(coll1,1,9);
PRINT_ELEMENTS(coll1,"coll1: ");
// transform elements of coll1 into coll2 with ten times their value
transform (coll1.begin(), coll1.end(), // source range
back_inserter(coll2), // destination range
bind2nd(multiplies<int>(),10)); // operation
PRINT_ELEMENTS(coll2,"coll2: ");
}
/*
coll1: 1 2 3 4 5 6 7 8 9
coll2: 10 20 30 40 50 60 70 80 90
*/