How to combine an cell array and a double array

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?

[Jan]

Please post an explicite example.

[yasmine]

example: x = {'USGG3M Index' 'USGG6M Index' 'USGG9M Index'}

how to convert it to a double matrix?

[Jan]

Dear yasmine: How do you want to convert 'USGG3M Index' to a double? What is the wanted result? NaN is the expected result as explained in "doc str2double".

[Geoff]

cellfun( @(s) str2double(regexp(s,'\d+','match')), x ) ???

[yasmine]

but this returns the number 3 only not the whole string USGG3M Index

Answer 1

[Jan]

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.

[yasmine]

Thanks a lot Jan for your time.

[Walter Roberson]

Tao Bi comments to Jan Simon:

Good explanation for how to store the numerics and the strings

[Vincent]

If I store values and column names in two different variables, is it in some way possible to combine both when saving to a txt file?

Here is an example:

header = {'m1','m2','m3'};
values = zeros(nSamples,3);
values(:,1) = m1;
values(:,2) = m2;
values(:,3) = m3;

here I want to combine both to a variable 'header_values'

save('output.txt','header_values','-ascii');

Thx for your answers

[Walter Roberson]

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]

Thank you for the quick answer. It worked perfectly well first converting the array to a table (array2table) and then save it with writetable(). :)

Answer 2

[Wayne King]

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);

[yasmine]

i have tried in your example, it worked. However, in the case of my exmaple, it gives me NaN

[Wayne King]

Jan's question is right on target, the problem is what kind of number do you think USGG3M is?

Answer 3

[Jan]

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.

[yasmine]

but this does not yield an array for a furtehr purpose to be combined with a double array

[Jan]

No array? What do you get as output?

[yasmine]

Dear Jan, i have tried the example of Wayne King and it works out for his example, so why it did not work for mine?

[Jan]

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]

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