# How to extract specific parts of a matrix

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lech king2021-3-26

In a 512 x 512 matrix where each cell has a number between 0 and 1000, a large part of the cells in this matrix, for example, contains the value 98 (on the left) and on the other side, a large number of cells contain, for example, the value 900.
In the case of when there is only one matrix, it is easy to determine what numbers the matrix contains on both sides.
But in other matrices these numbers are different
I'm looking for a way to automatically specify these numbers on both sides of a matrix

### 采纳的回答

Let's see if I understand what you're trying to do. As I understand it, you have a 512x512 matrix with lots of values of 98 on the left side and lots of 900 on the right side. And you want to automatically find the most common number on the left side of the matrix, and the most common number on the right side? Here's how I'd do that:
M = 1000*rand(512); % some random numbers between 0 and 1000
M(1:10:1e5) = 98; % every tenth value on the left side is 98
M(2e5:12:end) = 900; % every 12th value on the right side is 900
imagesc(M) % displays the matrix
It's difficult to see, because only 1 in 10 values on the left side ar 98, but still 98 is the most common value on the left side. And on the right side, the most common value is 900, because it's every 12th value. Here's how you'd find the most common value on the left and right side:
LeftSide = mode(M(:,1:256),'all')
LeftSide = 98
RightSide = mode(M(:,257:end),'all')
RightSide = 900
##### 3 个评论显示隐藏 2更早的评论
lech king 2021-3-28
Thank you very much for your help
It was exactly what I wanted
Excellent

### 更多回答（1 个）

Logical indexing would be an easy and fast solution.
##### 3 个评论显示隐藏 2更早的评论
lech king 2021-3-27
The problem is that in other matrices it is not clear which number has the highest number
In other words, the main problem is to determine the number that fills the most cells in the matrix

R2020a

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