Get vector of a specific member from a vector of structs

Question

I have a vector of structs as follows. The struct holds the relevant data for a plot.

struct DATA_T
{
    double x;
    double y;
    double z;
}

std::vector<DATA_T> results;

I need to be able to retrieve all the x values within results vector and store them as a vector of doubles

I know that I could create these vector programmatically.

std::vector<double> x_values;
x_values.reserve(results.size());
for(auto const &data : results)
{
    x_values.push_back(data.x);
}

However, I was wondering if there is a more concise solution. Perhaps using a similar approach to how I can search for specific data points using find_if?

you could use `std::transform`, but i doubt that it will be any faster or cleaner than what you already have, though you should reserve the right amount in the vector before calling `push_back` — 463035818_is_not_an_ai, Jul 28 '17 at 16:03
Possibly duplicate with [C++ std::transform vector of pairs->first to new vector](https://stackoverflow.com/questions/9094132/c-stdtransform-vector-of-pairs-first-to-new-vector) — duong_dajgja, Jul 28 '17 at 16:17

Edgar Rokjān · Accepted Answer · 2017-07-28T16:08:52.020

1

You could use std::transform for that providing it with appropriate lambda to retrieve x:

std::vector<double> x_values;
x_values.reserve(results.size());

std::transform(std::cbegin(results), std::cend(results),
    std::back_inserter(x_values),
    [](const auto& data) {
        return data.x;
    }
);

DEMO

edited Jul 28 '17 at 16:08

answered Jul 28 '17 at 16:03

Edgar Rokjān

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@iyop45 for this particular piece of code `std::transform` might be a good choice without loosing the readability. But in general case too many STL algorithms in a single place do no guarantee the readability at all :) – Edgar Rokjān Jul 28 '17 at 16:17

Get vector of a specific member from a vector of structs

1 Answers1