# How to extract sub-matrices from a big matrix?

6 views (last 30 days)
Mohamed Nedal on 21 Dec 2019
Edited: Stephen23 on 23 Dec 2019
Hello everyone,
I have two matrices, kindly find the attached file
soho ---> size = 23×12 , each row represents an event.
omni ---> size = 8760 × 17 , each row represent an hour (timeseries data).
The first three columns are, in order, "year", "month", "day".
I need to do the following operation:
if soho_day = omni_day
take that omni_day and the following 120 rows (hours) and put them as a separate matrix with a prefix (i.e., omniSUB_1).
and so on
I have these code blocks
% to find the matched date and store the that day along with the following 5 days (120 hours) in another matrix.
for n = 1:length(soho)
for m = 1:length(omni)
if datetime(soho(n,1),soho(n,2),soho(n,3),...
'Format','dd/MM/yyyy') == ...
datetime(omni(m,1),omni(m,2),omni(m,3),...
Format','dd/MM/yyyy')
for k = m:120
omniSUB{n,:} = omni(k,:);
end
end
end
end
and
% to create sub-matrices.
Prefix = 'omniSUB_';
for i = 1:Month_length
var_name = strcat(Prefix, num2str(i));
data_child = genvarname(var_name);
eval([data_child ' = omniSUB{i}']);
end
but I don't know how to put them together to do that operation. Please correct me.
Mohamed Nedal on 22 Dec 2019
I'll try the indexing approach. Thanks!

Ridwan Alam on 21 Dec 2019
Edited: Ridwan Alam on 21 Dec 2019
% to find the matched date and store the that day along with the following 5 days (120 hours) in another matrix.
for n = 1:size(soho,1)
omniRowInd = find(omni(:,1)==soho(n,1) & omni(:,2)==soho(n,2) & omni(:,3)==soho(n,3),1,'first');
if ~isempty(omniRowInd)
tempTable = omni(omniRowInd:min(omniRowInd+119,size(omni,1)),:);
eval(['omniSUB_' num2str(n) '=' 'tempTable;']);
end
end
Hope this helps!
Mohamed Nedal on 23 Dec 2019
Edited: Mohamed Nedal on 23 Dec 2019
Yes, you're right.
I found where's the error, it was a glitch in defining the date-time pairs and I corrected it.
Thank you!

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