Modify strings within a vector? (Without using loops) - c++

Question

I'm trying to take a vector of strings and remove every character that's not a letter (number, symbols, etc.) I'm also not trying to use loops.
So here's an example of a vector:
std::vector<std::string> a = {"he2llo*", "3worl$d"};
And I want the string returned to look like this:
std::vector<std::string> a = {"hello", "world"};
Right now I'm trying to use the transfrom and erase algorithms, but I can't get the syntax right.
This is obviously incomplete, but it's the basic setup of what I have so far:
int trim(std::vector<std::string> a){
std::transform(a.begin(), a.end(), a.erase())

Answer 1

You can use std::for_each on the vector and then use the erase-remove idiom on the strings, as follows
#include <vector>
#include <string>
#include <algorithm>
#include <iostream>
int main() {
std::vector<std::string> a = {"he2llo*", "3worl$d"};
std::for_each(a.begin(), a.end(),[](auto & str){
str.erase(std::remove_if(str.begin(), str.end(), [] (auto & character){return !isalpha(character);}), str.end());
});
for(auto const & el : a)
std::cout << el << " ";
}
The output:
hello world

Answer 2

Recursively..
#include <iostream>
#include <vector>
std::string remove_bad_characters(std::string input, std::string result)
{
if (input.size() == 0)
{
return result;
}
if (!isalpha(input[0]))
{
return remove_bad_characters(input.substr(1), result);
}
result += input[0];
return remove_bad_characters(input.substr(1), result);
}
std::vector<std::string> edit_bad_strings(std::vector<std::string> input, std::size_t index)
{
if (index == input.size())
{
return input;
}
input[index] = remove_bad_characters(input[index], "");
return edit_bad_strings(input, index + 1);
}
int main() {
std::cout<<remove_bad_characters("h!ello!", "")<<"\n";
std::vector<std::string> good = edit_bad_strings(std::vector<std::string>{"h!ell#o", "wo0rl-d"}, 0);
for (std::string str : good)
{
std::cout<<str<<" ";
}
return 0;
}

Answer 3

You can use std::for_each instead of loop to traverse each element.
Then you can apply std::transform on each element of vector.
You can refer -
http://www.cplusplus.com/reference/algorithm/for_each/
http://www.cplusplus.com/reference/algorithm/transform/

Answer 4

Here's one way you can do it with the algorithm header and lambda functions:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
int main() {
std::vector<std::string> strArr = {"he2llo*", "3worl$d"};
std::transform(strArr.begin(), strArr.end(), strArr.begin(), [](std::string &str) -> std::string {
str.erase(std::remove_if(str.begin(), str.end(), [](char chr) -> bool {
return ! isalpha(chr);
}), str.end());
return str;
});
std::for_each(strArr.begin(), strArr.end(), [](const auto &str) {
std::cout << str << '\n';
});
return 0;
}
The outer lambda processes each string to erase specific characters by using remove_if, while the inner lambda just controls which characters are removed. Whether that's more readable than a loop-based solution is open to debate :-)

Answer 5

You can use C++20 std::erase_if
#include<string>
#include<vector>
#include<iostream>
#include<algorithm>
int main() {
std::vector<std::string> a = {"he2llo*", "3worl$d"};
std::transform(a.begin(), a.end(), a.begin(),
[](auto& str) {
std::erase_if(str, [](const auto& chr){return !isalpha(chr);});
return std::move(str);
});
for (const auto& str: a){
std::cout << str << std::endl;
}
}

Answer 6

You can try it in different ways with STL <algorithm>s, i implemented a functor to process each word :
#include <iostream>
#include <vector>
#include <cctype>
#include <algorithm>
class Processing{
public:
std::string operator()(std::string& value){
for_each(value.begin(), value.end(), [&](char v) mutable throw() ->
void {
auto fetch = std::find_if( value.begin(), value.end(), [&](char v)mutable throw()->
bool{
return(!isalpha(v));
});
if(*fetch){
value.erase( fetch );
}
});
return value;
}
};
int main()
{
std::vector<std::string> values = {"44h%ello333","%w%or333ld21"};
std::for_each(values.begin(),values.end(), Processing());
std::for_each(values.begin(),values.end(), [](std::string& value)->
void {
std::cout<<value<<" ";
});
return 0;
}