How do I get rid of NaNs in MATLAB?

Question

I have files which have many empty cells which appear as NaNs when I use cell2mat , but the problem is when I need to get the average values I cannot work with this as it shows error with NaN. In excel it overlooks NaN values, so how do I do the same in MATLAB?

In addition, I am writing a file using xlswrite :

xlswrite('test.xls',M);

I have data in all rows except 1. How do I write:

M(1,:) = ('time', 'count', 'length', 'width')

In other words, I want M(1,1)='time' , M(1,2)='count' , and so on. I have data from M(2,1) to M(10,20) . How can I do this?

Answer 1

As AP correctly points out , you can use the function isfinite to find and keep only finite values in your matrix. You can also use the function isnan . However, removing values from your matrix can have the unintended consequence of reshaping your matrix into a row or column vector:

>> mat = [1 2 3; 4 NaN 6; 7 8 9]  % A sample 3-by-3 matrix

mat =

     1     2     3
     4   NaN     6
     7     8     9

>> mat = mat(~isnan(mat))  % Removing the NaN gives you an 8-by-1 vector

mat =

     1
     4
     7
     2
     8
     3
     6
     9

Another alternative is to use some functions from the Statistics Toolbox (if you have access to it) that are designed to deal with matrices containing NaN values . Since you mention taking averages, you may want to check out nanmean :

>> mat = [1 2 3; 4 NaN 6; 7 8 9];
>> nanmean(mat)

ans =

     4     5     6     % The column means computed by ignoring NaN values

---

EDIT: To answer your additional question on the use of xlswrite , this sample code should illustrate one way you can write your data:

C = {'time','count','length','width'};  % A cell array of strings
M = rand(10,20);                        % A 10-by-20 array of random values
xlswrite('test.xls',C);           % Writes C to cells A1 through D1
xlswrite('test.xls',M,'A2:T11');  % Writes M to cells A2 through T11

Answer 2

Use ' isfinite ' function to get rid of all NaN and infinities

A=A(isfinite(A))

%create the cell array containing the column headers columnHeader = {'Column 1', 'Column 2', 'Column 3', 'Column 4', 'Column 5',' '};

%write the column headers first xlswrite('myFile1.xls', columnHeader );

% write the data directly underneath the column headers xlswrite('newFile.xls',M,'Sheet1','A2');

Answer 3

Statistics Toolbox has several statistical functions to deal with NaN values. See nanmean, nanmedian, nanstd, nanmin, nanmax, etc.

Answer 4

您可以将NaN设置为任意数字，如下所示：

mat(isnan(mat))=7 // my lucky number of choice. 

Answer 5

May be too late, but...

x = [1 2 3; 4 inf 6; 7 -inf NaN];
x(find(x == inf)) = 0; //for inf
x(find(x == -inf)) = 0; //for -inf
x(find(isnan(x))) = 0; //for NaN