problems with a one-to-many join using a look up table

I have two datasets which I want to concatenate horizontally, for example:

A=[12 432 245 3000 500]
b=[3000 500 6.2 4.3 1.5]

I need to match b to A based on the last two columns of a and first two of b, so the answer would be:

c=[12 432 245 3000 500 3000 500 6.2 4.3 1.5]

A and b are different sizes. With A containing repeated values of the last two columns and b is acting as a look up table with all possible values.

I basically want to search through A and when number in column 4 and 5 is the same as the numbers in b column 1 and 2 I want to append the following values in b (a one-to-many join)

I hope that made sense, any help would be appreciated

[the cyclist]

Definitely not clear to me. For the single example you give

c = [A,b]

seems to be what you say you want. But, I'm guessing that is not really what you want.

I think you would be much better off if you post two or three small examples of inputs, and the outputs that you want from those inputs.

[Jan]

The physical meaning of the values does not matter. I still do not understand what you want to achieve. Please show an example, where "multiple entries in A which share the same Indexes".

Answer 1

[the cyclist]

I don't have time to think about a full-blown solution right now, but let me suggest you take a look at the ismember() command, and in particular the 'rows' option. This command should allow you to identify rows that are common between A and b, which you can then concatenate. Type

doc ismember

in the command window to see the documentation.

[Lucy]

Thanks for the advice, I will take a look at this command

[the cyclist]

Just finding a few more minutes to think about your problem. I think, but I am not sure, that you want to do something like

[tf,idx] = ismember(b(:,[1 2]),A(:,[4 5]),'rows')

to identify the rows where the first two columns of b are included in the last two columns of A.