How to convert time domain to frequency domain using FFT

I have the data in time domain. I want to convert it into frequency domain. Can someone please provide a code for the sam? Thankyou. It will be a great help

Answer 1

[KSSV]

data = importdata("before test.txt") ; 
t = data(:,1) ; 
amp = data(:,2) ; 

dt = unique(diff(t)) ; % time step 
Fs = 1/dt ;             % sampling frequency 
L = length(t) ; 
Y = fft(amp) ; 

P2 = abs(Y/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);
f = Fs*(0:(L/2))/L;

subplot(121)
plot(t,amp) ;
xlabel('time')
ylabel('amp')
%
subplot(122)
plot(f,P1) 
title('Single-Sided Amplitude Spectrum of X(t)')
xlabel('f (Hz)')
ylabel('|P1(f)|')

[Sanketh Shetty]

Thank you so much for your answer. I also needed to compare the before and after FFT of the data like for example like this

[KSSV]

Edited the answer.

[KSSV]

OP commented: Thank you so much again.

[KSSV]

Thanks is accepting the answer.

[Leen Mazen]

Dear KSSV

Thanks for code , but could you please explain below (p1 and p2):

P2 = abs(Y/L);

P1 = P2(1:L/2+1);

P1(2:end-1) = 2*P1(2:end-1);

f = Fs*(0:(L/2))/L;

what is the required to use it ?