CODEWITHSUNDEEP
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user_1_1_1
user_1_1_1

Reputation: 923

Fetching a subset of array in the prescribed order

I have a master array and a query array:-

master_array=[2;5;3;7;1];
query_array=[1;3];

All elements of query array will be a member of the master array. That is a rule. I have to find the order of all the elements of query array as prescribed by the master array.

I could naively do this:-

a=[];
for i=query_array'
a=[a;i,find(master_array==i)];
end
a=sortrows(a,2);
order_array=a(:,1);

Is a more efficient solution available?

Upvotes: 1

Views: 26

Answers (2)

gnovice
gnovice

Reputation: 125874

You could use intersect:

order_array = intersect(master_array, query_array, 'stable');

Or you could use ismember:

order_array = master_array(ismember(master_array, query_array));

Upvotes: 2

Tommaso Belluzzo
Tommaso Belluzzo

Reputation: 23685

This solution takes almost 70% less time in my benchmarks:

[~,idx] = ismember(master_array,query_array);
order_array = query_array(idx(idx > 0));

For more information about the ismember function, refer to this page of the official Matlab documentation.

Upvotes: 1

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