Find the earliest common date and indicator of two date vectors.

Hi,

I have got two date vectors: a=[28.02.2019;01.03.2019;04.03.2019;...] and b=[01.03.2019;04.03.2019;...]

How to find the earliest common date (=01.03.2019) and its vector index indicator (for date vector a is 2 and b is 1).

Thank you in advance for any suggestions.

[Guillaume]

"I have got two date vectors"

Please use valid matlab syntax for your examples.

In matlab a date vector is a 1x3 or 1x6 vector containing only 1 date.

a = [28.02.2019; 01.03.2019; 04.03.2019];

is not valid matlab syntax. So what do you have?

[BdS]

Thank you for your code suggestion.

I have got a 55x1 datetime date vector which is vector A and a 56x1 datetime date vector which is vector B.

The date format is 06-Mar-2019

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It does not have to be that the time vector A is always smaller than Vector B. It can change. It can also be that the first date of time vector A begins later than in date vector B. It must be flexible.

Answer 1

[Guillaume]

intersect will give you all the dates common to a and b. By default, it also sorts them, so the first of these will be the earliest one, so:

[commondates, whereina, whereinb] = intersect(a, b);
firstcommon = commondates(1);
whereina = whereina(1);
whereinb = whereinb(1);

Answer 2

[Rik]

This answer assumes you have your dates in a datetime format. If you don't it should be relatively easy to convert to it. If your release is too old to support it, please comment with what release you're using.

a=datetime([2019 2019 2019],[2 3 3],[28 1 4]);
b=datetime([2019 2019 2019],[3 3 5],[1 4 1]);

[common_dates,ind_in_a]=ismember(a,b);
common_dates=a(common_dates);
[first,a_min_ind]=min(common_dates);
a_ind=find(ind_in_a==a_min_ind);
b_ind=find(b==first);

[BdS]

Thank you for code. As I mentioned above, it is not for all cases valid. see my comments above.

[Rik]

For what cases doesn't this work? This code does not assume equal length of the vector. It works for most shapes that have no zero-length dimension.

[BdS]

With your code I get for a the indicator 1 and for b 1 as well.

I should actually get for a indicator 2 and b indicator 1. Both indicates 01-Mar-2019 in vector a and b.

The code should also work in cases when b begins with an earlier date.

[Rik]

I edited my answer. It works now, but it has become messy, so I would suggest you keep using Guillaume's solution.