How to join two numeric arrays into a single string?

Hi guys, I have a situation that: I have one vector A, say 10000x1, and another vector B 10000x1, both are numerical arrays with floating point numbers in it. Now I want to write the data into one line of string as below:

A(1):B(1) A(2):B(2) ....A(10000):B(10000)

Is there an efficient way to do this? Right now, i am just using a for loop, change the floating number to string first, than add the ':', and then concatenate them together. This is very slow. Could anybody help? Thanks a lot.

Answer 1

[Azzi Abdelmalek]

A=rand(10,1);
B=rand(10,1);
out=sprintf('%f:%f ',A,B)

[Yi Zhu]

Hi Azzi, thanks for your quick reply, it works like charm. But if A are all integers (from 1 to N), how to do the same thing? I use out=sprintf('%d:%f ',A,B)

The output is: 1:2.00000 3:4.00000 .....

It seems that it only print A, there is no B show up. thanks.

[Stephen23]

@Yi Zhu: if it doesn't give the correct result, then why did you accept this answer?

See my answer for the correct solution.

[Yi Zhu]

@stephen: This solution is correct to my initial problem, when A and B are both double vector, so I accept it.But soon I had trouble when A is integer vector, so I asked again. Thanks for your time and efforts, I appreciate it.

[Stephen23]

@Yi Zhu: this doesn't give the correct solution according to your original question, because the order is wrong This answer actually gives an output in order of A(1):A(2) A(3):A(4)... B(1):B(2) B(3):B(4)... which is definitely not the order that you specified in your question: A(1):B(1) A(2):B(2).... You just didn't check it properly:

>> A = [0;1;2;3;4];
>> B = [5;6;7;8;9];
>> out = sprintf('%d:%d ',A,B)
out = 0:1 2:3 4:5 6:7 8:9

As I wrote in my answer, the correct solution (to match the order in your question) is to concatenate the two vectors beforehand.

Answer 2

[goerk]

I don't know if its faster but you can try

 str = [sprintf('%f:',A) sprintf('%f:',B)];
 str(end) = [];

[Yi Zhu]

Hi goerk, thanks for your quick reply, your solution also works. But same problem, if A are all integers (from 1 to N), how to do the same thing? I use out=sprintf('%d:%f ',A,B)

The output is: 1:2.00000 3:4.00000 .....

It seems that it only print A, there is no B show up. thanks.

Answer 3

[Stephen23]

The correct solution is to first concatenate the matrices (and because you have column matrices you also need to transpose):

>> A = [0;1;2;3;4];
>> B = [5;6;7;8;9];
>> sprintf('%d:%d ',[A,B].')
ans = 0:5 1:6 2:7 3:8 4:9

Note that evaluating this string to generate a numeric vector will be very inefficient:

http://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

and a much better solution is to use arrayfun:

 >> C = arrayfun(@(a,b)a:b,A,B,'Uni',false);
 >> [C{:}]
 ans =
    0   1   2   3   4   5   1   2   3   4   5   6   2   3   4   5   6   7   3   4   5   6   7   8   4   5   6   7   8   9

[Yi Zhu]

Thanks for the detailed answer. But still, when A is integer vector, B is double vector,

A = 1:10
B = randn(10,1)
sprintf('%d:%d ',[A,B].')

The result is

1:2 3:4 5:6 7:8 9:10 6.088942e-01:8.072232e-01 4.285545e-01:8.931010e-01 4.249390e-01:4.236594e-01 6.304087e-01:1.888050e-01 4.633747e-01:9.932405e-01

It is not what I want, I want the integer and double to interleave together. Could you show me how to do this? Thanks a lot.

BTW, I want the double to be shown in double format, not in the scientific 'e-' form.

[Stephen23]

>> A = (1:10).';
>> B = randn(10,1);
>> sprintf('%d:%f ',[A,B].')
ans = 1:-0.356415 2:0.039756 3:-2.294004 4:0.555082 5:-1.860219 6:1.430920 7:-0.423892 8:-1.010463 9:0.515073 10:-0.2211
28

And read the fprintf documentation for more information on defining the format string.

[Yi Zhu]

Thanks @Stephen, it works. Thank you very much.