MATLAB Answers


How to find the maximum value for each 24 rows in an array?

Asked by Behzad Navidi on 4 Nov 2019
Latest activity Answered by Behzad Navidi on 14 Nov 2019 at 9:29
I have a 3d array, precip= :,:, 8760. in fact 8760 rows are available in one column. I want to find the maximum value in this column 24-by-24 in rows. And saving the bigger value and eliminate the smaller one. and do it for all 8760-row
so if the dimension before doing this is precip = :, :, 8760, after this work should be precip = :, :, 365.
I wanna practical this for a 3d array which the third dimension is what I talking about.
I'm attaching all my array. as the volume of original file is so big I cut first 72 rows and attach it
Thank you


Dear Shubham,
Sorry for the delayed reply, I was really sick.Thank you for your comment.
Actually, this 3D dimension represents: longitude*latitude*time
all this data represents hourly maximum temperature for a certain area in a year. the time is hourly so it has 87600 values. but I want to have a daily maximum temperature so I need to pick the biggest value of 24 hours (it is a maximum temperature of all day)
I want to divide third dimension 24-by-24 (day by day) and then selecting the maximum of every 24 values. in this way, after doing that I have a 3d array in which the third dimension has 365 or 366(leap years) values.
I uploaded a little sample of my data. here is the link if you can download 68.7 MB:
Thank you again
Let's take a example with an array of dimension 2x3x4. So time = 1hr, 2hr, 3hr & 4hr. At each hour let's assume random data for temp & assume that on this earth 1 day is of 2hr.
t = 1hr
T = [20 30 40
50 60 70];
t = 2hr
T = [30 50 70
80 90 75];
t = 3hr
T = [-20 40 10
15 900 80];
t = 4hr
T = [25 55 11
10 -45 9];
What is the output that you are expecting in this hypothetical situation? I understand your 3rd dimesion (pages) will be 2 but I still don't know what do you want to do with the 1st & 2nd dimesion. I am expecting your output to be:
Day = 1
T = ??
Day = 2
T = ??
ok if assume that on this earth 1 day is of 2hr, then the output is:
Day = 1
T = 90
Day = 2
T = 900
I don't want to change the first and second dimensions.
input = :, :, 87600
output = :, :, 365 or 366

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2 Answers

Answer by Shubham Gupta on 14 Nov 2019 at 0:19
Edited by Shubham Gupta on 14 Nov 2019 at 0:26
 Accepted Answer

According to the comments, you have provided, this will produce the desired output :
yd = max(max(mn2t)); % first find maximum for each hour
y = reshape(yd,24,1,size(yd,3)/24); % reshape it by day
output = max(y); % find maximum of each day
Let me know if this works !


Dear Shubham,
It's works perfect for the array. thank you so much. I gonna accept your answer but webpage says: An Error Occurred (Unable to complete the action because of changes made to the page. Reload the page to see its updated state)
I have faced this error previously, and I know a few hours later it will be fixed and I can click on accept answer.
but now just in a case do you know how to use this code when mn2t is cell (34*1 cell) (instead of an array) and using this code for all 34 rows of this cell (the cell consists of 34 of this 3d array?
Thank you - I will accept your answer.
Simply use for loop mn2t:
output = cell(size(mn2t));
for i = 1:length(mn2t)
mn2t_mat = mn2t{i}; % extract matrix of ith element
yd = max(max(mn2t_mat)); % first find maximum for each hour
y = reshape(yd,24,1,size(yd,3)/24); % reshape it by day
output{i} = max(y); % find maximum of each day
Output will be cell vector with each cell containing maximum of each cell of mn2t.

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Answer by Behzad Navidi on 14 Nov 2019 at 9:29

Thank you 🌹


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