array: concatenate two columns of integers to one colum

(Matlab novice)

I thought this would be so easy...

I have a 2-d array of integers and I want to combine two columns like this:

... 123 456 ...

... 123 456 ...

etc...

I want:

... 123456 ...

... 123456 ...

etc...

as single numbers (that is, I want (123 * 1000) + (456)

The number of rows will be variable from one run to the next.

Any help would be appreciated.

[Jan]

The question is not clear. What is the wanted output for: [1,2,3,4; 5,6,7,8; 9,10,11,12] ?

Answer 1

[Honglei Chen]

a = randi([1 100],[5 4])  % a 5x4 integer matrix
b = cellfun(@num2str,{a(:,2:3)},'UniformOutput',false)
c = cellfun(@(x) strrep(x,' ',''), cellstr(b{1}),'UniformOutput',false)
a(:,2) = str2double(c)
a(:,3) = []

[Jan]

Faster:

b = sprintf('%d%d*', a(:, 2:3).');
c = sscanf(b, '%d*');  [EDITED, thanks Honglei]

STRREP operates on cell string directly, so there is usually no need to create a time-consuming anonymous function inside CELLFUN.

[Honglei Chen]

@Jan, thanks for the tip. That's a good one. I think you missed a b in your second expression.

Answer 2

[Tom]

 A=[1 2 3;3 5 7];
B=[7 8 9;4 5 6];
%
C=[A B];
w=size(C,2);
D=10.^(w-1:-1:0);
Out=sum(bsxfun(@times,D,[A B]),2)

Answer 3

[Jan]

A = [1234, 567;  1, 234];
B = A(:, 1) .* nextpow10(A(:, 2)) + A(:, 2);

function Y = nextpow10(X)
Y = 10 .^ floor(log10(abs(n)) + 1);  % [EDITED]

Please test this before using, I cannot run Matlab currently.

[Andrei Bobrov]

A=randi(67,6,4)
n = ceil(log10(A(:,2:end)));
out = sum(A(:,1:end-1).*(10.^fliplr(cumsum(fliplr(n),2))),2)+ A(:,end)

Answer 4

[William Sampson]

Yeah - so

1) I'm not getting it and

2) I seem to not have been clear enough (sorry...)

what I have is a data array with 59 columns and an indeterminate number of rows and I want to combine 2 (for example) columns as described above. In reality it is 5 columns, 8 - 12, of 16 digits each, but I'll start with getting 2 of them done.

So I have, e.g., rawData(:,9) and rawData(:,10) to combine

[Honglei Chen]

It's the same. I updated my answer to show an example of combining 2nd and 3rd column of a matrix

[Jan]

See my suggestion:

B = rawData(:, 9) .* nextpow10(rawData(:, 10)) + rawData(:, 10)
result = [rawData(:, 1:8), B, rawData(:, 11:end)]

I do not see, why the suggested method should not work.

Btw. What do you expect as result of two 16 digit numbers? You can store only 16 digits in variables of the type DOUBLE.

Answer 5

[Ryan]

A = [1234, 567;  1, 234]; %Sample Data

% Figure out how many spaces to shift the left column
C = ceil(log10(A(:,2)));

% Find areas where the value is a multiple of 10 or is 1
idx = A(:,2) == 1 | rem(A(:,2),10) == 0;
C(idx) = C(idx) + 1; % Handle the exception

% Determine how much to shift the left column
C = 10.^C;

% Add in the right column
A = A(:,1).*C + A(:,2);