How to aplly a function to all columns?

Question

Gabriel Aguirre 2023-1-22

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https://ww2.mathworks.cn/matlabcentral/answers/1898590-how-to-aplly-a-function-to-all-columns

回答： dpb 2023-1-22

Hi guys, i have a code which do fft, however are so many columns to apply this code i need a way to do it faster, i already see something about cellfun, but this did't work. my data comes from vibration, I have a column of time and the rest of vibration data.

the following function makes the fft, psd now i want to apply to all columns of an excel table (csv).

function [freq_ax,fft_ax, psd_ax] = my_fft(t,ax)
%% computando fft
dt = mean(diff(t));
n = length(t);
L = 1:floor(n/2);
freq = 1/(dt*n)*(0:n-1);
fhat = (fft(ax,n)*1/(n-1));
fft_ax = abs(fhat(L));
freq_ax = (freq(L));
psd = fhat.*conj(fhat);
psd_ax = psd(L);
end 

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Answer 1

dpb 2023-1-22

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https://ww2.mathworks.cn/matlabcentral/answers/1898590-how-to-aplly-a-function-to-all-columns#answer_1153940

See fft -- in particular, note the first comment...

"fft(X) is the discrete Fourier transform (DFT) of vector X. For matrices, the fft operation is applied to each column."

Hence, you get the operations applied to all columns for free; just pass the vibration data array (without augmenting it with the time which is of no import for the FFT, all you need is the sample rate) to FFT and operate by column for the rest. You'll get N PSDs; one per column.