# plot histogram without using matlab hist() function

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ws 2011 年 12 月 22 日
Hi all
There is a function called hist(), but if I want to plot a graph without using hist() command, how to plot a graph? I means using command to do the job same as hist().
Thank you.

#### 2 件のコメント

Aditi Shetty 2018 年 8 月 19 日
a=rgb2gray(A);
subplot(3,1,1);
imshow(a);
title('original image');
[r,c]=size(a);
z=zeros(1,256);
for i=1:r
for j=1:c
b=a(i,j);
z(b+1)=z(b+1)+1;
end
end
N=sum(z);
p=zeros(1,256);
s=zeros(1,256);
c=zeros(1,256);
r=zeros(1,256);
for k=1:256
p(k)=z(k)/N;
if k==1
c(k)=p(k);
s(k)=c(k)*255;
r(k)=floor(s(k));
else
c(k)=c(k-1)+p(k);
s(k)=c(k)*255;
r(k)=floor(s(k));
end
end
subplot(3,1,3)
stem(r,z)
title('histogram')
Ritvik Ramesh Palvankar 2019 年 9 月 10 日
Can you explain me the code after "for k=1:256". I did not understand the part where you took s(k)=c(k)*255
Also, why is zero matrix used and why is c(k-1) added to p(k)

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### 採用された回答

Naz 2011 年 12 月 22 日
It depends on how you want to bin your data and what kind of data you have.
The idea of hist function is similar to stacks of coins: Let's say you have a bag of coins and after you separate them by values and stack on one another, you will get different heights. The hist function does the same.
data=[1 3 5 7 4 8 0 1 3];
If you want to distribute your data into 10 bins, you would create a new array of size 10:
histArray=zeros(1,10); % prealocate
x=0:1:9;
then, you would run a forloop to count how many times you encounter in a particular value:
for n=1:length(data)
histArray(1,data(n)+1)=histArray(1,data(n)+1)+1; % every time you meet the particular value, you add 1 into to corresponding bin
end
bar(histArray)
There could be another case. Let's say you want to distribute your data into 5 bins only (0 and 1 go in the 1st bin, 2 and 3 go in the 2nd...). In this case, you would run the same loop but with more complicated conditioning:
histArray=zeros(1,5);  %prealocate
x=0:2:8 % create bin numbers for plot
for n=1:length(data)
histArray(1,floor(data(n)/2)+1)=histArray(1,floor(data(n)/2)+1)+1;
% every time you meet the particular value
%you add 1 into to corresponding bin
end
bar(x,histArray)
You can design your own hist function to fit you needs

#### 2 件のコメント

ws 2011 年 12 月 22 日
thanks, this is what i'm looking for.. :)
Anna Kasdan 2018 年 10 月 7 日
Hi! I am trying to do this with data that includes negative numbers, and I get the error 'Subscript indices must either be real positive integers or logicals.' Any thoughts? The data I am working with is:
n = 200; a = 0; b = 2; data = b.* randn(1, n) + a;

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### その他の回答 (1 件)

Adrian Lukasik 2015 年 5 月 13 日

hello I have another problem. The same thing, but in 3D: There is a function called hist3(), but if I want to plot a graph without using hist3() command, how to plot a graph? I means using command to do the job same as hist3(). I have matrix b, 2x1000, and the task about making histogram plot without hist3() function.
Thank you.

#### 1 件のコメント

Walter Roberson 2015 年 5 月 13 日
You should open a new Question for that.
Once you have the counts for each grid-point, use bar3()

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