How to make a list of appearance

Hi guys,

I am having some lists of animal which some animal appear many time in many list. So I want to count the appearance of animal and show how many times it appear, then save it to excel file

the data after saving in excel shoulbe be like this

name , count

a 1

b 3

c 2

I have think about 2d- char array but it seems Matlab does not support it.

Answer 1

[Ameer Hamza]

Use findgrpups() and histcounts(). Something like this

names = ["cat" "dog" "cat" "cat" "dog"];
[n, unique_names] = findgroups(names);
freq = accumarray(n(:), 1);
T = table(unique_names(:), freq(:));

Result

>> T
T =
  2×2 table
    Var1     Var2
    _____    ____
    "cat"     3  
    "dog"     2  

Write to excel file

writetable(T, 'filename.xlsx')

In R2019a and later, following will also work

names = ["cat" "dog" "cat" "cat" "dog"];
[freq, unique_names] = groupcounts(names(:));
T = table(unique_names(:), freq(:));

[R G]

thank you!, it works great. I just dont understand that it seems you count the appearance separately from the name, so why the names and values of appearance are not tangled

[Ameer Hamza]

I am glad to be of help!

It works smoothly because of the way findgroups returns the two outputs. For example, 2nd output contains ["cats" "dogs"], so the 1st output will replace all cats with 1 and dogs with 2. Therefore, when I apply histcount, the order remains the same again.

However, I just realized that the current code could fail if the number of unique animals' names are large. I have updated the code to cover that condition too.

[R G]

That is situation that I am also worrying about ( the number of unique animals' names are large). But your update code get error, please kindly recheck it.

Error using table (line 233)
All table variables must have the same number of rows.
Error in xxxx_testCode (line 55)
T = table(unique_names(:), freq(:)); 

[Ameer Hamza]

Ah! I didn't try to run the code after changing. Try the updated code now. I have now used another function.

[R G]

Thank you, it works well now!!!

[Ameer Hamza]

I am glad to be of help!

Answer 2

[KSSV]

Let str be your list of animals.

xbins = unique(str);
[counts,centres] = hist(str,xbins);
R = [centres counts']

Answer 3

[Steven Lord]

histcounts and histogram can handle categorical arrays.

names = ["cat" "dog" "cat" "cat" "dog"];
animals = categorical(names);
[counts, types] = histcounts(animals);
results = table(types.', counts.', 'VariableNames', ["animal", "population"])