How to combine an cell array and a double array

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yasmine
yasmine 2012-3-22
评论： Vincent 2020-7-24
i am trying to convert a cell array (consisting of strings) into a double array in order to be able to combine it with a double array (matrix) (consisting of numbers)using str2double but it gives me NaN? is there another solution?
[EDITED, Jan Simon, important information from a comment]:
Example:
x = {'USGG3M Index' 'USGG6M Index' 'USGG9M Index'}
how to convert it to a double matrix?
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Geoff
Geoff 2012-3-22
cellfun( @(s) str2double(regexp(s,'\d+','match')), x ) ???
yasmine
yasmine 2012-3-25
but this returns the number 3 only not the whole string USGG3M Index

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回答（3 个）

Jan
Jan 2012-3-25
You cannot insert strings in a double array in Matlab. A double array consists of doubles, as the name says already.
A cell can contain elements of different types:
C = {'Header1', 'Header2'; ...
17, 8.15};
But of course C is not a double array anymore. The usual method to store numerical arrays and names for the columns is using two different variables.
Your question could not be answered sufficiently for three days now, because you do not post the required details inspite of repeated questions for clarifications. This is inefficient.
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Walter Roberson
Walter Roberson 2020-7-24
save() supports -append that can add more to the end of a text file.
However, save -ascii does not support cell array of character vectors, and if you try to save -ascii of a plain character vector then it will convert the characters to numbers.
dlmwrite() can write character vectors, but you have to abuse its 'precision' option pretty badly to do that.
The realistic options are:
  1. fopen() / fprintf() the header / fclose, after which you can save -ascii of just the numbers
  2. fopen() / fprintf() everything / fclose, which can produce any text format you want
  3. Use a table() object with the headers as the variable names, and writetable()
  4. Convert everything into a cell array, one header or one number per cell, and use writecell()
These days I would typically use writetable() unless I had specialized output format needs; if I had specialized needs then tricks like dlmwrite() are just not worth it, and fprintf() with a custom format is best.
Vincent
Vincent 2020-7-24
Thank you for the quick answer. It worked perfectly well first converting the array to a table (array2table) and then save it with writetable(). :)

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Wayne King
Wayne King 2012-3-22
I think you should give us a very simple concrete example with MATLAB code.
x = {'2','3','4'};
y = cellfun(@str2double,x,'uni',false);
y = cell2mat(y);
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yasmine
yasmine 2012-3-22
i have tried in your example, it worked. However, in the case of my exmaple, it gives me NaN
Wayne King
Wayne King 2012-3-22
Jan's question is right on target, the problem is what kind of number do you think USGG3M is?

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Jan
Jan 2012-3-22
C = {'3.14159265', '1.414562373095'};
D = sscanf(sprintf('%s,', C{:}), '%g,');
This is still faster than using a C-mex to convert the single strings.
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Jan
Jan 2012-3-22
Because 'USGG3M Index' is not the string representation of a number, in opposite to '2' or '2.3'. Please explain what you expect as result of converting 'USGG3M Index' to a double. This core point of your question is not clear.
My example is working also, btw.
yasmine
yasmine 2012-3-25
i want to make a new array that contains a cerain output (double array) and has a heading USGG3M Index. accordingly, in order to concatenate (merge) these two array, they have to be double. regards

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