MATLAB Answers


Unique rows of 2 cells with 2 columns each.

Asked by BdS
on 13 Sep 2019
Latest activity Commented on by Guillaume
on 18 Sep 2019
I have got 2 cells with 2 columns each:
I am looking of the unique values of each cells in form of (nr. of unique values in first row x 2 columns)
I tried the following 2 codes:
I get the unique values in dim (nr. of unique values x 1 column). However, I would like get the output with the second column.
Do you have any suggestions?


I understand "containing the unique values" as containing for example:
column1 = {'1 HK Equity';
'10 HK Equity';
'101 HK Equity';
'1038 HK Equity';
'11 HK Equity';
I understand "nr. unique value" as the count of each unique value, so:
column1 = [2;
so I'm confused as to what you want.
I am sorry for the confusion.
I mean as your wrote in your first example. But with the corresponding value in column 1
The unique values should be based on the information based on column 1

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2 Answers

Answer by Matt J
on 13 Sep 2019
 Accepted Answer

I tried the following 2 codes: unique(vertcat(IdxMembers,IdxMembers2),'rows')... I get the unique values in dim (nr. of unique values x 1 column).
No, you really should have gotten 2 column output, as in the example below. Something about your situation must be different from what you are describing.
>> [IdxMembers,IdxMembers2] =deal( randi(3,4,2) , randi(3,3,2))
IdxMembers =
2 1
2 2
3 2
3 2
IdxMembers2 =
3 3
3 2
1 1
>> unique(vertcat(IdxMembers,IdxMembers2),'rows')
ans =
1 1
2 1
2 2
3 2
3 3


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Answer by Guillaume
on 17 Sep 2019
Edited by Guillaume
on 17 Sep 2019

merged = [new; old]; %simpler way to write vertcat(new, old)
[~, row] = unique(merged(:, 1)); %get row index of unique values in the 1st column
result = merged(row, :) %extract these rows


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The 'rows' option of unique does not work with cell arrays. It gives you a warning if you try to do it (in my opinion, it should throw an error):
>> result = unique([new; old], 'rows');
Warning: The 'rows' input is not supported for cell array inputs.
> In cell/unique>celluniqueR2012a (line 236)
In cell/unique (line 148)
However, the 'rows' option does work with string arrays, so another option would be to convert your cell arrays of char vectors into string arrays (requires R2016b or later):
result = unique(string([new; old]), 'rows');
You can then keep working with the string array or if you really want to convert back to cell array:
resultcell = cellstr(result);
thank you for your explanation.
Option 1 seems to more efficient: 0.007129 seconds in comparison with 0.028908
Option 1 seems to more efficient: 0.007129 seconds
As long as you consider efficiency to be just the execution speed and that you care about a few milliseconds difference.
Indeed string arrays may have a slight speed impact but if you consider that if you'd used string arrays to start with your original code would have worked straight away but instead it took you 4 days to resolve the problem, in term of development time string arrays would have won hands down.

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