将元素附加到数组的最快方法是什么? [英] What is the fastest way of appending an element to an array?

问题描述

这是如何将元素附加到 MATLAB 中的数组? 该问题解决了如何 将元素附加到数组的问题.那里讨论了两种方法:

This is a follow-up question to How to append an element to an array in MATLAB? That question addressed how to append an element to an array. Two approaches are discussed there:

A = [A elem]  % for a row array
A = [A; elem] % for a column array

和

A(end+1) = elem;

第二种方法有一个明显的优势，即兼容行和列数组.

The second approach has the obvious advantage of being compatible with both row and column arrays.

然而，这个问题是:这两种方法中哪一种最快?我的直觉告诉我第二种方法是，但我想要一些支持或反对的证据.有什么想法吗?

However, this question is: which of the two approaches is fastest? My intuition tells me that the second one is, but I'd like some evidence for or against that. Any idea?

推荐答案

第二种方法(A(end+1) = elem)更快

根据以下基准(使用 timeit 来自 File Exchange 的基准测试函数)，第二种方法(A(end+1) = elem)更快，因此应该是首选.

The second approach (A(end+1) = elem) is faster

According to the benchmarks below (run with the timeit benchmarking function from File Exchange), the second approach (A(end+1) = elem) is faster and should therefore be preferred.

有趣的是，这两种方法之间的性能差距在旧版 MATLAB 中比在较新版本中要小得多.

function benchmark

    n = logspace(2, 5, 40);
    % n = logspace(2, 4, 40); 
    tf = zeros(size(n));
    tg = tf;

    for k = 1 : numel(n)
        x = rand(round(n(k)), 1);

        f = @() append(x);
        tf(k) = timeit(f);

        g = @() addtoend(x);
        tg(k) = timeit(g);
    end

    figure
    hold on
    plot(n, tf, 'bo')
    plot(n, tg, 'ro')
    hold off
    xlabel('input size')
    ylabel('time (s)')
    leg = legend('y = [y, x(k)]', 'y(end + 1) = x(k)');
    set(leg, 'Location', 'NorthWest');
end

% Approach 1: y = [y, x(k)];
function y = append(x)
    y = [];
    for k = 1 : numel(x);
        y = [y, x(k)];
    end
end

% Approach 2: y(end + 1) = x(k);
function y = addtoend(x)
    y = [];
    for k = 1 : numel(x);
        y(end + 1) = x(k);
    end
end

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