Fourier analysis – Spectrum of harmonic amplitude

I have simulated an electric machine in mathematica in discrete calculus. One of the results is three-phase currents. My answer is as follows:
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Now, I'm looking for the harmonic amplitude spectrum of the current of one of the phases, for example phase A as in the following figure:
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I must mention that, as all my simulations are in discrete computation, the current phase response is a vector like:

ia = {0, 0., -0.548775, <<14995>>, 11.4906, 10.9900, 11.1094}

Thanks in advance