在matlab中获取唯一元素的计数及其计数

Question

我有这个向量可以说

A = [1; 2; 3; 1; 2; 3; 1; 2; 3]

我怎样才能找到类似这样的独特元素及其数量？

1 = 3
2 = 3
3 = 3

我绝对可以遍历各个元素并使用一些幼稚的技术。我不想要那种解决方案，因为我的真实数据将在数百万范围内，所以我不能只遍历每个元素。

在matlab中最有效的方法是什么？

Answer 1

为了提高效率，这很难超越：

elements = unique(A);
counts = histc(A(:), elements);

Answer 2

Notlikethat's answer 是要走的路。但是它的效率（计算时间）实际上可以提高：

sA = sort([A(:); inf]); %// sort A
ind = diff(sA)~=0; %// index of last element of each run of equal values
elements = sA(ind); %// unique elements
counts = diff([0; find(ind)]); %// lengths of runs

基准测试：

clear all
A = randi(100,1e6,1); %// Example data. Large column vector

%// Notlikethat's answer
tic
elements = unique(A);
counts = histc(A(:), elements);
toc

clear elements counts

%// This answer
tic
sA = sort([A(:); inf]);
ind = diff(sA)~=0;
elements = sA(ind);
counts = diff([0; find(ind)]);
toc

Elapsed time is 0.175594 seconds.
Elapsed time is 0.076032 seconds.