How can I match rows from two tables by timestamp and create a new table?

I am working with two sets of data that have timestamps that do not match up exactly, but I need to join the table rows by matching the timestamps that are approximately 30 minutes apart. Here is an example of the two different tables, and the end result that I am looking for:

T1 = 

Obs             Time                Var1               Var2             Var3              Var(n)...
1            2/2/2017 11:00           1                  2                3                     
2
3
4
...

T2= 

Obs             Time                Var4   
1            2/2/2017 10:40           1                            
2

I am hoping to have a matched table that will look like this:

T3 = 

Obs        Time (from T1)    Time (from T2)        Var1          Var2          Var3        Var4(from T2)
1
2
3

Answer 1

[Guillaume]

Assuming R2016b, convert your tables to Timetables and use withtol to match rows. This assumes that all rows of the first table will be match:

tt1 = table2timetable(t1);
tt2 = table2timetable(t2);
s = withtol(tt1.Time, minutes(30));
joinedtt = [tt1, tt2(s, 'Var4')]

[William Pierce]

Sorry, I should have clarified that the tables do not have the same number of rows. So we are essentially filtering out unwanted data from T1 by matching timestamps to T2

[Walter Roberson]

Yes, withtol() can help with that. https://www.mathworks.com/help/matlab/matlab_prog/subscript-into-times-of-timetable.html

You would give the T2 timestamps as input to the withtol() and then use the output of the withtol() to index T1

[Guillaume]

As Walter says, if there can be non-matched rows in both tables:

tt1 = table2timetable(t1);
tt2 = table2timetable(t2);
S = withtol(tt1.Time, minutes(30));
tt2 = tt2(S, :);
S = withtol(tt2.Time, minutes(30));
joinedtt = [tt1(S, :), tt2(:, 'Var4')]

ought to work (as long as no two rows in one table match the same row in the other).

[William Pierce]

will this also work with version 2015a?

[Walter Roberson]

Sorry, timetables() are new in R2016b.