How to count the occurrence of numbers in certain value range (show 0 if no occurrence)

Question

Yunwei 2023-11-9

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回答： Steven Lord 2023-11-9

采纳的回答： John D'Errico

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Hello everyone,

I konw that I can use function groupcounts to count the occurrence of values.

However I would like to count the times a value appear within a range of values, and if there is no occurrence, it should show 0.

For example, I want to count number occurence between 0 to 20 in array A, while there is no value 10 in A, the output I hope is the 10th cell as 0, but not skipped as using the function groupcounts.

Example:

P=[1 1 3 4 5 6 6 7 7 8 10];

if I run groupcounts

GB=groupcounts(P');

what I get GB is

What I hope to get as output is

Does anyone know how to code this?

Thanks a lot in advance!

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Answer 1

John D'Errico 2023-11-9

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编辑：John D'Errico 2023-11-9

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The simple answer is you want to use the wrong tool. Yes, it looks like you want to use groupcounts. But you don't.

P=[1 1 3 4 5 6 6 7 7 8 10];
Counts = accumarray(P',1)
Counts = 10×1
     2
     0
     1
     1
     1
     2
     2
     1
     0
     1

Easy peasy. Yes, with an extra step, you could have used groupcounts. But why, when one line does what you want?

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Yunwei 2023-11-9

Thanks John!

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Answer 2

Steven Lord 2023-11-9

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If your data is sorted you could use histcounts. In the case of your sample data, where all the values are integers, I'm going to use the "integers" BinMethod.

P=[1 1 3 4 5 6 6 7 7 8 10];
[counts, edges] = histcounts(P, "BinMethod", "integers")
counts = 1×10
     2     0     1     1     1     2     2     1     0     1
edges = 1×11
    0.5000    1.5000    2.5000    3.5000    4.5000    5.5000    6.5000    7.5000    8.5000    9.5000   10.5000

To identify the bin centers rather than the edges:

centers = edges(1:end-1)+diff(edges)./2
centers = 1×10
     1     2     3     4     5     6     7     8     9    10

If you have non-integer data you might need to explicitly create the bin edges. You can use the unique function for this, but be careful about the last bin (which includes both edges, not just the left edge.)