How to use an array as an indexing table to add search result as a new row to the querying array ?

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Hi, :
I thank you at first.
My question is , 'How to use an array as an indexing table to add search result as a new row to the querying array ?'
For example, the Q matrix is 1000 x 1, the Idx matrix is 5 x 3, as below:
Idx =
1 2 10
2 3 20
3 4 30
4 5 40
5 6 50
Then use Q( : ) every cell to search Idx by the logical expression, " if Idx(1 , 1 , : ) < Q(:,1) < Idx(1, 2 , :) "
,to search which row will the Q(:) be located, then return the columns 3 of the Idx(,,3) respectively to store every it in Q by added a new column 2.
For example Q(1) = 3.5, then Idx(3, 1) = 3, Idx(3, 2) = 4, so that " Idx(3, 1) < Q(1) < Idx(3, 2)", so the Q(1) should have the returned result from Idx's column3 = 30, then store this '30', to a new column2 to Q(1,2) = '30'
Is it possible to avoid using loop, or any existing similar function to simplify it ?
Thank you very much.
Best regards.

Accepted Answer

Andrei Bobrov
Andrei Bobrov on 24 Jul 2019
Edited: Andrei Bobrov on 24 Jul 2019
Q_new = [Q,Idx(discretize(Q,[Idx(:,1);Idx(end,2)]),3)];
  9 Comments
Tamura Kentai
Tamura Kentai on 24 Jul 2019
Hi, Andrei:
I beg your pardon.
I discovered it after I tried some successfully.
Is it possible, to get an interpolating value between 2 index ?
For example, if the indexing value of Q(1) is 3.5, which is the middle value of the row4 & row5, then return the value (40 -30) * ( (3.5 -3) / (4-3) ) + 30 = 35 .
Thank you very much.
Best regards.
>> [Inew(:,1) Inew(:,3)]
ans =
-Inf NaN
1 10
2 20
3 30
4 40
5 50
6 NaN

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More Answers (1)

Tamura Kentai
Tamura Kentai on 24 Jul 2019
Hi, Andrei:
I'm sorry, after some hours, I think I have one solution. It's the following:
% index_array_search.m
load('Idx.mat');
load('Q.mat');
Idx = [(1:5)',(2:6)',10*(1:5)'];
Inew = [-inf,1,nan;Idx;6,inf,nan];
[~,ii] = histc(Q,[Inew(:,1);Inew(end,2)]);
out = [Q,Inew(ii,3),Inew(ii+1,3), Inew(ii,1), Inew(ii+1, 1)];
out = [out,( ( out(:,1)-out(:,4) ).*( out(:,3) - out(:,2) ) ./ (out(:,5)-out(:,4)) + out(:,2) )];
I add those necessary for computing into the array.
It looks pretty fine.
Thank you for the ideas.
Best regards.
>> index_array_search
>> out
out =
1.1000 10.0000 20.0000 1.0000 2.0000 11.0000
2.2000 20.0000 30.0000 2.0000 3.0000 22.0000
3.3000 30.0000 40.0000 3.0000 4.0000 33.0000
4.4000 40.0000 50.0000 4.0000 5.0000 44.0000
5.5000 50.0000 NaN 5.0000 6.0000 NaN
  3 Comments
Tamura Kentai
Tamura Kentai on 25 Jul 2019
Hi, Andrei:
In fact, I am thinking if there are other options other than 'linear', actually I mean it's 'linear' distribution in log-log plane.
For example, if plot the 'y=-x' using 'loglog(x,y)', the line will be straight, but if add some constant offset, eg: 'y=-x + 500', the plot 'loglog(x,y)', it won't be straight line in log-log plane.
If you think it's interesting. In fact I have tried survey ,but no good result except using manually adjusting such math equations.
Thank you very much.
Best regards.

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