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如何计算矩阵中给定值的元素数量？

发布于 2024-09-02 13:07:25 字数 155 浏览 5 评论 0原文

有谁知道如何计算一个值在矩阵中出现的次数？

例如，如果我有一个 1500 x 1 矩阵 M （向量），它存储工作日 (1 - 7) 的值，我如何计算有多少个周日 (1)、周一 (2)、 ... , 星期六(7) 存储在 M 中？

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最冷一天 2024-09-09 13:07:25

查看确定和计数数组的唯一值。

或者，要计算 5 出现的次数，只需执行以下操作

sum(your_matrix == 5)

Have a look at Determine and count unique values of an array.

Or, to count the number of occurrences of 5, simply do

sum(your_matrix == 5)

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春花秋月 2024-09-09 13:07:25

以下是我能想到的计算唯一元素的所有方法的列表：

M = randi([1 7], [1500 1]);

选项 1：制表

t = tabulate(M);
counts1 = t(t(:,2)~=0, 2);

选项 2：hist/histc

counts2_1 = hist( M, numel(unique(M)) );
counts2_2 = histc( M, unique(M) );

选项 3：accumarray

counts3 = accumarray(M, ones(size(M)), [], @sum);
%# or simply: accumarray(M, 1);

选项 4：sort/diff

[MM idx] = unique( sort(M) );
counts4 = diff([0;idx]);

选项 5：arrayfun

counts5 = arrayfun( @(x)sum(M==x), unique(M) );

选项 6：bsxfun

counts6 = sum( bsxfun(@eq, M, unique(M)') )';

选项 7：稀疏

counts7 = full(sparse(M,1,1));

Here's a list of all the ways I could think of to counting unique elements:

M = randi([1 7], [1500 1]);

Option 1: tabulate

t = tabulate(M);
counts1 = t(t(:,2)~=0, 2);

Option 2: hist/histc

counts2_1 = hist( M, numel(unique(M)) );
counts2_2 = histc( M, unique(M) );

Option 3: accumarray

counts3 = accumarray(M, ones(size(M)), [], @sum);
%# or simply: accumarray(M, 1);

Option 4: sort/diff

[MM idx] = unique( sort(M) );
counts4 = diff([0;idx]);

Option 5: arrayfun

counts5 = arrayfun( @(x)sum(M==x), unique(M) );

Option 6: bsxfun

counts6 = sum( bsxfun(@eq, M, unique(M)') )';

Option 7: sparse

counts7 = full(sparse(M,1,1));

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万劫不复 2024-09-09 13:07:25

一次对所有值 1 到 7 执行此操作的一种方法是使用函数 ACCUMARRAY：

>> M = randi(7,1500,1);  %# Some random sample data with the values 1 through 7
>> dayCounts = accumarray(M,1)  %# Will return a 7-by-1 vector

dayCounts =

   218       %# Number of Sundays
   200       %# Number of Mondays
   213       %# Number of Tuesdays
   220       %# Number of Wednesdays
   234       %# Number of Thursdays
   219       %# Number of Fridays
   196       %# Number of Saturdays

One way you can perform this operation for all the values 1 through 7 at once is to use the function ACCUMARRAY:

>> M = randi(7,1500,1);  %# Some random sample data with the values 1 through 7
>> dayCounts = accumarray(M,1)  %# Will return a 7-by-1 vector

dayCounts =

   218       %# Number of Sundays
   200       %# Number of Mondays
   213       %# Number of Tuesdays
   220       %# Number of Wednesdays
   234       %# Number of Thursdays
   219       %# Number of Fridays
   196       %# Number of Saturdays

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