count the number a letter appears in a string and plot a histogram

I have to write a function that counts the number a base of DNA repeats itself inside of a string and then plot a histogram with the function 'histogram'. Here is my code to find the number of bases and it works fine

n=length(s);
if n>1000  
    disp('errore dimensione');
    return
end
A=0;
C=0;
G=0;
T=0;
for i=1:n
    switch s(i)
        case 'A'
            A=A+1;
            
        case 'C'
            C=C+1;
            
        case 'G'
            G=G+1;
            
        case 'T'
            T=T+1;
            
        otherwise
            disp('questo non è DNA');
            return
            
       
    end
end
vec=[A , C , G , T];

From here i want a histogram with x-axis representing the letters and y-axis representing the frequency each letter appears inside a string, how can i do that?

Answer 1

[Stephen23]

V = categorical(["A","C","G","T"]);
W = V(randi(4,1,23))

W = 1×23 categorical array
     G      T      C      C      T      T      T      T      C      A      G      C      G      G      C      T      T      A      C      A      G      A      C 

histogram(W)

Answer 2

[DGM]

I'm sure there are text analysis tools for this, but here's one basic way.

categories = 'ACGT';

% generate a test string
N = 20; % length of test string
teststr = categories(randi([1 numel(categories)],1,N))

teststr = 'GCTAGTATAAGGTTGAGAGG'

% find character frequencies
% if you just want character counts, don't divide
freq = sum(teststr == categories.',2)/numel(teststr)

freq = 4×1

0.3000 0.0500 0.4000 0.2500

% display as a bar chart
bar(freq)
xticklabels(num2cell(categories))