Combining cell array and double vector into sprintf

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David Mueller
David Mueller 2018-5-18
回答： Guillaume 2018-5-18
I would like to create a string for a plot annotation. My needs: Create annotation of the following format:
a1 = number
b1 = number
c1 = number
a2 = number
etc.
Where a1,b1, etc. come from a cell array and the numbers come from a vector. I would do it all manually but I am creating a large number of graphs and the number of coefficients changes between each plot.
What i would like to do is something like the following:
coeffnote = []
for l = 1:length(coeffVals)
coeffnote = [coeffnote, coeffNames(l) ' = ' num2str(coeffVals(l)) '\n'];
coeffnote = string(coeffnote);
end
sprintf(coeffnote(:))
When I run this, I keep getting an error. I am at my wits' end with this. Can anyone help.

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回答（4 个）

Stephen23
Stephen23 2018-5-18
编辑：Stephen23 2018-5-18
You don't need a loop at all, it is simpler without one:
str = {'aa','bb','cc'};
vec = 1:3;
tmp = [str;num2cell(vec)];
out = sprintf('%s = %d\n',tmp{:});
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David Mueller
David Mueller 2018-5-18
Oh okay, I was transposing the wrong one I guess. Thanks! Also - and this is a small matter - is there a simple way to remove the return on the final line?
Stephen23
Stephen23 2018-5-18
编辑：Stephen23 2018-5-18
"is there a simple way to remove the return on the final line?"
In my experience the simplest way is to put such character/s at the start and remove the first one/s:
out = sprintf('\n%s = %d',tmp{:});
out = out(2:end);
You could do something similar with the last newline, but I find this way easier to follow.

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Aditya Adhikary
Aditya Adhikary 2018-5-18
编辑：Aditya Adhikary 2018-5-18
Another answer based on your code (not caring about efficiency):
coeffVals = [1,2,3];
coeffNames = {'a1','b1','c1'};
coeffnote = [];
for i = 1:length(coeffVals)
val = coeffVals(i);
name = coeffNames(i);
x = [name,' = ',num2str(val),'\n'];
x = strjoin(x);
coeffnote = [coeffnote, x];
end
sprintf(coeffnote);
  2 个评论
David Mueller
David Mueller 2018-5-18
Perfect! Thanks! Just out of curiosity, what would a more efficient way be? I feel like Stephen Cobeldick's answer was very close, but giving a weird output.
Jan
Jan 2018-5-18
Letting the output grow iteratively is a bad programming practice in general, because the costs grow exponentially.

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KSSV
KSSV 2018-5-18
x = rand(10,1) ;
y = rand(10,1) ;
plot(x,y,'.r') ;
hold on
str = cell(10,1) ;
for i = 1:10
str{i} = sprintf(['c',num2str(i),'=',num2str(i)]) ;
end
text(x,y,str)
  1 个评论
Stephen23
Stephen23 2018-5-18
编辑：Stephen23 2018-5-18
@KSSV: what is the point of using both num2str and sprintf ? Your use of sprintf here does absolutely nothing. This does the same thing:
['c',num2str(i),'=',num2str(i)]
Note that it would be more efficient to use sprintf rather than num2str:
sprintf('c%d = %d',i,i)

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Guillaume
Guillaume 2018-5-18
I'm surprised nobody's mentioned compose which is the modern, more powerful, easier to work with, version of sprintf. Going back to Stephen's example:
str = {'aa','bb','cc'};
vec = 1:3;
compose('%s = %d', string(str(:)), vec(:))
Note that the (:) are to ensure the inputs are column vectors. If they already are, you don't need to bother.

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