# How to find the index of any maximum matrix?

2 views (last 30 days)
vimal kumar chawda on 9 Jul 2021
Commented: DGM on 11 Jul 2021
I need the index or position in column and row of the maximum value.
X =rand(20)
How can I ?
Image Analyst on 11 Jul 2021
Wow, 107 tags, if I conted correctly. I think that must be a reconrd. It must have taken you more time to enter all those than to just look up max() in the help. I'll show you how to do it in my answer below.
Stephen23 on 11 Jul 2021
You might not use tags, but you are not the only user of this forum, and some of us certainly do use tags.

DGM on 9 Jul 2021
Edited: DGM on 9 Jul 2021
s = [10 10];
x = randi(100,s)
x = 10×10
40 81 9 67 90 11 44 79 79 56 2 53 68 82 7 42 35 39 51 95 60 22 51 18 47 6 44 83 38 49 57 44 87 24 6 41 59 83 53 94 74 54 17 10 43 2 72 27 16 46 18 60 91 20 13 24 77 38 9 21 22 8 47 100 70 7 42 88 27 17 79 69 38 11 59 80 79 89 68 10 92 92 77 89 49 64 98 97 74 61 50 69 93 52 28 43 4 61 15 96
[~,idx] = max(x(:)) % this gets the linear index
idx = 37
[row col] = ind2sub(s,idx) % if you want subscripts instead
row = 7
col = 4
Of course, that's only the first instance of the maximal value.
Image Analyst on 11 Jul 2021
Actually since his question used randn() which will give unique floating point values and only one max value, not several, your suggestion to use max() is fine.
DGM on 11 Jul 2021
I just used randi so that the matrix was easier to read by eye and fit better on the page. The fact that it allows for frequent duplicates was what prompted me to mention the behavior.

Image Analyst on 11 Jul 2021
m = randi(9, 5, 5)
maxValue = max(m(:))
% Find out what rows and columns the max occurs in.
% Works even if the max occurs in more than one place
% unlike the index the second output argument of max() gives you.
[rowsOfMax, columnsOfMax] = find(m == maxValue)
You'll see:
m =
3 5 7 9 8
7 9 3 5 3
6 4 5 2 8
2 6 7 2 3
2 3 9 3 9
maxValue =
9
rowsOfMax =
2
5
1
5
columnsOfMax =
2
3
4
5
Like I said, it's a more robust solution than using max() alone.

### Categories

Find more on Logical in Help Center and File Exchange

R2021a

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!