Compare two tables with two column combinations

I have two tables, say:

t1 = table(categorical({'a';'b';'c';'c';'a';'b'}),categorical({'d';'e';'d';'f';'e';'d'}),[1;2;3;4;5;6],datetime({'2017-1-1 12:00 AM','2017-1-3 10:20 AM','2017-1-3 1:36 PM','2017-1-4 9:45 AM','2017-1-6 12:00 AM','2017-1-7 12:12 PM'})')
t2 = table(categorical({'a';'a';'c';'b';'c'}),categorical({'f';'d';'e';'f';'d'}),[5;4;3;2;1],datetime({'2017-1-1 12:00 AM','2017-1-3 6:20 AM','2017-1-3 1:36 PM','2017-1-4 9:45 AM','2017-1-6 12:10 AM'})')

t1 =

6×4 table

    Var1    Var2    Var3            Var4        
    ____    ____    ____    ____________________

    a       d       1       01-Jan-2017 00:00:00
    b       e       2       03-Jan-2017 10:20:00
    c       d       3       03-Jan-2017 13:36:00
    c       f       4       04-Jan-2017 09:45:00
    a       e       5       06-Jan-2017 00:00:00
    b       d       6       07-Jan-2017 12:12:00

t2 =

5×4 table

    Var1    Var2    Var3            Var4        
    ____    ____    ____    ____________________

    a       f       5       01-Jan-2017 00:00:00
    a       d       4       03-Jan-2017 06:20:00
    c       e       3       03-Jan-2017 13:36:00
    b       f       2       04-Jan-2017 09:45:00
    c       d       1       06-Jan-2017 00:10:00

Now I want the result or the rownumbers of every combination of the first two columns in t2 that are not in t1

How can I do this?

*Edited question with a little more complicated table

Answer 1

[Peter Perkins]

tables have all the same "set membership" functions as numeric arrays:

>> t1 = table({'a';'b';'c';'c';'a';'b'},{'d';'e';'d';'f';'e';'d'});
>> t2 = table({'a';'a';'c';'b';'c'},{'f';'d';'e';'f';'d'});
>> [t3,i1] = setdiff(t1,t2)
t3 =
  4×2 table
    Var1    Var2
    ____    ____
    'a'     'e' 
    'b'     'd' 
    'b'     'e' 
    'c'     'f' 
i1 =
     5
     6
     2
     4

[Aletta Wilbrink]

Thank you.

But what if I have a third column (with numbers or dates) and I don't want that one in the comparison?

[Guillaume]

Well, then you use

[~, i1] = setdiff(t1(:, [1 2]), t2(:, [1 2]));
t3 = t1(i1, :)

[Bradley Stiritz]

Hi Peter,

Your answer is very elegant, thank you. Do you have any thoughts please on also checking for differences in value vs. not-a-value status -- i.e. NaN, NaT ?

Would you recommend working along the lines of e.g. varfun(@isnan..)) ?

Thanks,

Brad

Answer 2

[Star Strider]

If I understand what you want to do, this will work:

Lv = ismember(t2, t1, 'rows');
DesiredRows = find(~Lv)

DesiredRows =
     1
     3
     4

If not, reversing the arguments to ismember (link) will work.