Unique changing order(unique output values are reshuffled)

i have cell array with data like '2/6/2009','2/6/2009','2/6/2009','2/6/2009','2/7/2009',,'2/7/2009','2/7/2009','2/8/2009','2/8/2009','2/8/2009'

if i make use of unique to get only unique values the order is getting reshuffled

getting output like : '2/8/2009','2/6/2009','2/7/2009'

Desired output format: '2/6/2009','2/7/2009','2/8/2009'

[Stephen23]

Simply using my FEX submission natsort:

>> C = {'2/6/2009','2/6/2009','2/6/2009','2/6/2009','2/7/2009','2/7/2009','2/7/2009','2/8/2009','2/8/2009','2/8/2009'};
>> D = natsort(unique(C));
>> D{:}
ans = 2/6/2009
ans = 2/7/2009
ans = 2/8/2009

But the best solution is to change the date format for an ISO 8601 date format, which sort correctly into chronological order when you do a character sort. Once you start using ISO 8601 date formats you simply avoid all of these trivial problems.

Answer 1

[Muruganandham Subramanian]

b={'2/6/2099','2/6/2099','2/6/2099','2/6/2099','2/7/2099','2/7/2099', '2/7/2099','2/8/2099','2/8/2099','2/8/2099','2/10/2099','2/10/2099', '2/12/2099'};

c=datevec(b);
c(:,4:6)=[];
c(:,4)=c(:,1);
c(:,1)=[];
d=num2str(c);
d=cellstr(d);
d=unique(d)

Check this above code. But it's not effective way to do..here In unique(), it's not chosing in random way, it considers the data of first,which is sorted minimum(i.e. '10' is first than '6').

[Walter Roberson]

Right. It looks character by character, and '1' comes before '6' so '10' sorts before '6'

[shaz]

Thanks

[Andrei Bobrov]

M = datevec(b,'mm/dd/yyyy');
[Muq, ii] = unique(M,'rows','first');
out = b(sort(ii));

[shaz]

thanks a lot

Answer 2

[Muruganandham Subramanian]

>>b={'2/6/2009','2/6/2009','2/6/2009','2/6/2009','2/7/2009','2/7/2009','2/7/2009',
'2/8/2009','2/8/2009','2/8/2009'};

>> c=unique(b)

>> c = 

      '2/6/2009'    '2/7/2009'    '2/8/2009'

Are you expecting this?

[shaz]

b={'2/6/2099','2/6/2099','2/6/2099','2/6/2099','2/7/2099','2/7/2099', '2/7/2099','2/8/2099','2/8/2099','2/8/2099','2/10/2099','2/10/2099', '2/12/2099'};

c=unique(b)

the output is

c= '2/10/2099' '2/12/2099' '2/6/2099' '2/7/2099' '2/8/2099'

which is in a random way

Answer 3

[Jan]

With a modern Matlab version you can use:

c = unique(b, 'first');

[Stephen23]

Or option 'stable'.

Answer 4

[Sebastian]

I know it's a bit late for an answer, but maybe it helps others. If you want to preserve the order of the input of 'unique', you can use the second return parameter. Like that it works for arbitrary data (i.e. strings and numerals, basically every data type 'unique' supports):

a = {'2/6/2009' '2/6/2009' '2/6/2009' '2/7/2009' '2/7/2009' '2/7/2009' '2/8/2009' '2/8/2009' '2/8/2009'};
[~, uIdx] = unique(a);
a(sort(uIdx))

This snippet does the following: Store the indices of the unique elements of 'a' in 'uIdx'. Then return the elements of 'a' from the first to the last using 'sort'.

[Jan]

The problem of shaz was, that he wanted a specific numerical order, in which '6' appears before '10'. Therefore the data must be converted from string to double, such that the sorting works.

Answer 5

[Steven Lord]

Convert your date data into a datetime array, then call unique (with or without the 'stable' flag) on the datetime array.

C = {'2/6/2009','2/6/2009','2/6/2009','2/6/2009','2/7/2009','2/7/2009', ...
     '2/7/2009','2/10/2009','2/8/2009','2/8/2009'};
D = datetime(C, 'InputFormat', 'MM/dd/uuuu')
unique(D)
unique(D, 'stable')

For purposes of this example I assumed your dates were days in February 2009. If they were the second of each month from June through October (without September) of 2009 swap the MM and dd sections of the InputFormat parameter.

[Stephen23]

"For purposes of this example I assumed your dates were days in February 2009. If they were the second of each month from June through October (without September) of 2009 swap the MM and dd sections of the InputFormat parameter."

Or avoid this pointless and confusing ambiguity entirely by using ISO 8601 dates.