有没有更优雅的替代品可以替代此MATLAB循环? [英] Is there a more elegant replacement for this MATLAB loop?

问题描述

我想更好地在MATLAB中向量化我的循环.目前，我正在尝试计算int列表中值的出现次数.我的代码与此类似:

I want to get better at vectorizing my loops in MATLAB. At the moment, I'm trying to count the occurrences of values in a list of ints. My code is similar to this:

list = [1 2 2 3 1 3 2 2 2 1 5];
occurrence_list = zeros(1,max(list));

for x=list
    occurrence_list(x) = occurrence_list(x) + 1;
end

是否有一个简单的向量化替代for循环? (或者我缺少一个内置的MATLAB函数吗?)我正在非常小的数据集上执行此操作，因此时间不是问题.我只想改善我的MATLAB编码风格.

Is there a simple vectorized replacement for that for loop? (Or is there a built in MATLAB function that I'm missing?) I'm doing this on pretty small data sets, so time isn't an issue. I just want to improve my MATLAB coding style.

推荐答案

除了HIST/HISTC函数之外，您还可以使用ACCUMARRAY来计算发生次数(以及许多其他聚合操作)

In addition to the HIST/HISTC functions, you can use the ACCUMARRAY to count occurrence (as well as a number of other aggregation operations)

counts = accumarray(list(:), 1)
%# same as: accumarray(list(:), ones(size(list(:))), [], @sum)

另一种方法是使用统计工具箱中的TABULATE(返回值，计数，频率):

Another way is to use TABULATE from the Statistics Toolbox (returns value,count,frequency):

t = tabulate(list)
t =
            1            3       27.273
            2            5       45.455
            3            2       18.182
            4            0            0
            5            1       9.0909

---

请注意，如果值不是从1m开始，或者在最小值和最大值之间存在较大差距的情况下，在计数之间会出现很多零.而是使用:

---

Note that in cases where the values don't start at 1m or in case there's large gaps between the min and the max, you will get a lot of zeros in-between the counts. Instead use:

list = [3 11 12 12 13 11 13 12 12 12 11 15];
v = unique(list);
table = [v ; histc(list,v)]'

table =
     3     1
    11     3
    12     5
    13     2
    15     1

代表唯一值及其计数(这只会列出至少出现一次的值)

representing the unique values and their counts (this will only list values with at least one occurrence)

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