Finding Indices of Duplicate Values
141 visualizzazioni (ultimi 30 giorni)
Mostra commenti meno recenti
Suppose, I have a variable,
a{1}=[
2 2 1 3
5 2 1 1
5 2 1 4
5 2 1 2
1 1 2 1
2 2 2 1
1 1 3 4
1 1 3 3
4 1 3 5
1 1 4 3
1 1 4 4
1 1 4 1
2 2 4 1
2 2 4 2
4 1 4 2
4 1 4 6
2 2 5 2
2 2 5 6
4 1 5 1
4 1 5 2
4 1 5 6
4 1 5 5]
How can I find the indices of duplicate values for column 3:4?
I am using Matlab R2013a. Thank you in advance.
0 Commenti
Risposta accettata
Simon
il 19 Nov 2013
Hi!
You may use "unique". The second output is the index of all unique values, e.g. in column 3. All other indices are duplicates.
6 Commenti
Jeffrey Daniels
il 1 Ott 2018
This is one solution but it is not complete or 100% accurate. The question asked for unique matches in columns 3 and 4. Also, this method only returns values that are repeated adjacent to each other. If you want to find all matches in all rows, I would refer you to this solution: https://www.mathworks.com/matlabcentral/answers/175086-finding-non-unique-values-in-an-array
Più risposte (2)
B Mohandes
il 10 Nov 2016
by coincidence i found another way to do it, but thanks to those who answered already. the outputs of the command "unique" can be tricky to deal with, hence, here is a straight forward way.
>> find(hist(a,unique(a))>1)
the command (hist) counts the frequency (number of repetitions) of a certain value in a vector. if you use: hist(a), matlab will divide the whole range of values to 10 periods, and count the repetitions of values lying within these ranges. however, if you use: hist(a,b), then the repetitions are counted against the reference (b). so when you count the occurrences of each element in (a) against the unique elements of (a), and you find the results that are >2, then you're finding the elements that occurred more than once.
regards
4 Commenti
RST
il 14 Mag 2024
If I understand correctly, you want the row indices where the pair a{1)}(3,4) are duplicated.
a{1}=[
2 2 1 3
5 2 1 1
5 2 1 4
5 2 1 2
1 1 2 1
2 2 2 1 % me!
1 1 3 4
1 1 3 3
4 1 3 5
1 1 4 3
1 1 4 4
1 1 4 1
2 2 4 1 % and me!
2 2 4 2
4 1 4 2 % and me!
4 1 4 6
2 2 5 2
2 2 5 6
4 1 5 1
4 1 5 2 % and me!
4 1 5 6 % and me!
4 1 5 5]
[~,ixu] = unique( a{1}(:,3:4), 'rows'); % gives indices of the first of the unique rows
ixd = setdiff( 1:size(a{1},1), ixu); % (duplicate rows) = (all rows) - (unique rows)
clear ixu
ixd
% show rows that are duplicates in columns 3:4
a{1}(ixd, :)
0 Commenti
Vedere anche
Categorie
Scopri di più su Creating and Concatenating Matrices in Help Center e File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!