FFT from a excel file

From the question title it seems that it is obtained by reading an Excel file, so likely the format/type has been messed up there. You could change the format to double with for example str2double (if the obtained data type happens to be a string), do check what's in that variable though (famous Excel® issue of converting values to nonsensical dates).

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Arnav Dabak 2023-6-1

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I checked the data type and it is double and I am reading it from an excel file.

I have attached a screenshot of the error.

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Answer 2

Star Strider 2023-6-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1976769-fft-from-a-excel-file#answer_1248534

编辑：Star Strider 2023-6-1

在 MATLAB Online 中打开

EDIT — (1 Jun 2023 at 16:07)

The array is table apparently created by readtable. Use cell array indexing (explained below) or refer to it as:

xdft = fft(channel1Data2.Ampl);

or:

xdft = fft(channel1Data2.{:,2});

The cell array indexing approaches will also work, so I will leave that part of my original Answer unchanged.

—

It could be that ‘channel1Data2’ is a cell array. If so, converting it to a numeric array should work —

channel1Data2 = num2cell(rand(10,2))
channel1Data2 = 10×2 cell array
    {[0.4233]}    {[0.9203]}
    {[0.8342]}    {[0.4878]}
    {[0.0641]}    {[0.7609]}
    {[0.4819]}    {[0.8762]}
    {[0.2812]}    {[0.1188]}
    {[0.5806]}    {[0.8916]}
    {[0.7699]}    {[0.4074]}
    {[0.9036]}    {[0.8791]}
    {[0.9735]}    {[0.3604]}
    {[0.6840]}    {[0.7983]}
xdft = fft(cell2mat(channel1Data2(:,2)));               % Use 'cell2mat'
xdft
xdft = 
   6.5008 + 0.0000i
   0.4475 - 0.0261i
   0.0448 - 0.2162i
   0.3068 + 0.8035i
   1.2347 + 0.3965i
  -1.3651 + 0.0000i
   1.2347 - 0.3965i
   0.3068 - 0.8035i
   0.0448 + 0.2162i
   0.4475 + 0.0261i
xdft = fft([channel1Data2{:,2}]).';                     % Cell Array Addressing (With Subsequent Transpose)
xdft
xdft = 
   6.5008 + 0.0000i
   0.4475 - 0.0261i
   0.0448 - 0.2162i
   0.3068 + 0.8035i
   1.2347 + 0.3965i
  -1.3651 + 0.0000i
   1.2347 - 0.3965i
   0.3068 - 0.8035i
   0.0448 + 0.2162i
   0.4475 + 0.0261i
xdft = fft(vertcat(channel1Data2{:,2}));                % Cell Array Addressing (With 'vertcat')
xdft
xdft = 
   6.5008 + 0.0000i
   0.4475 - 0.0261i
   0.0448 - 0.2162i
   0.3068 + 0.8035i
   1.2347 + 0.3965i
  -1.3651 + 0.0000i
   1.2347 - 0.3965i
   0.3068 - 0.8035i
   0.0448 + 0.2162i
   0.4475 + 0.0261i
xdft = fft(channel1Data2(:,2));                         % Numeric Array Addressing Of 'cell' Array (Reproduces The Error)
Error using fft
Invalid data type. First argument must be double, single, int8, uint8, int16, uint16, int32, uint32, or logical.
xdft