How to join two numeric arrays into a single string?

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Yi Zhu
Yi Zhu 2016-5-20
编辑： Stephen23 2016-5-20
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.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2016-5-20
A=rand(10,1);
B=rand(10,1);
out=sprintf('%f:%f ',A,B)
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Yi Zhu
Yi Zhu 2016-5-20
@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
Stephen23 2016-5-20
编辑：Stephen23 2016-5-20
@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.

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更多回答（2 个）

goerk
goerk 2016-5-20
I don't know if its faster but you can try
str = [sprintf('%f:',A) sprintf('%f:',B)];
str(end) = [];
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Yi Zhu
Yi Zhu 2016-5-20
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.

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Stephen23
Stephen23 2016-5-20
编辑：Stephen23 2016-5-20
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
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Stephen23
Stephen23 2016-5-20
编辑：Azzi Abdelmalek 2016-5-20
>> 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.

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