Generating matlab array from two arrays

Question

I have two large arrays which I will illustrate using the following examples.

The first array A is:

The second array B is:

I want to obtain the final array C as following:

[ 1 21 26;
  4 12 121;
  5 65 54];

i.e. use the common elements of first column from A and B to sieve out the rows I want to extract from arrays A and B and generate C.

Luis Mendo · Accepted Answer · 2014-05-19 17:07:57Z

2

Use the two-output vesion of ismember:

[ii jj] = ismember(A(:,1), B(:,1));
C = [ A(ii,:) B(jj(ii),2) ];

Note that in the second line ii is a logical index, whereas jj(ii) is a standard (integer) index.

edited May 19, 2014 at 17:07

answered May 19, 2014 at 17:01

Luis Mendo

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1 Comment

Stewie Griffin Over a year ago

Congratz Luis! Your 1000th answer!

Divakar · Accepted Answer · 2014-05-19 17:34:14Z

2

bsxfun approach -

%// Slightly bigger and not-so-straightforward example to avoid any confusion
    A =[ 1 21;
    3 4;
    4 12;
    8 10
    5 65]

B = [ 1 26;
    31 56;
    4 121;
    5 54
    9 99
    8 88]

binmat = bsxfun(@eq,A(:,1),B(:,1).');%//'
[v1,v2] = max(binmat,[],2);
C = [A(any(binmat,2),:) B(nonzeros(v1.*v2),2:end)]

Output -

A =
     1    21
     3     4
     4    12
     8    10
     5    65

B =
     1    26
    31    56
     4   121
     5    54
     9    99
     8    88


C =
     1    21    26
     4    12   121
     8    10    88
     5    65    54

edited May 19, 2014 at 17:34

answered May 19, 2014 at 17:08

Divakar

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6 Comments

Luis Mendo Over a year ago

Our approaches give different results if for example the last two rows of B are interchanged. The OP should have clarified. But from the wording, it would appear order doesn't matter?

Luis Mendo Over a year ago

... Or perhaps you are missing a .' within bsxfun?

Divakar Over a year ago

yeah that might be it! Thanks! My system running slow, I have like 30 something tabs open! And now I need to do some more processing.

Luis Mendo Over a year ago

I think you then need an any (because ind is now a column): C = [A(any(ind),:) B(...,2:end)]. And to index into B you may also need some changes; any(ind) may not work

Luis Mendo Over a year ago

The party wouldn't be he same without bsxfun:-)

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