Ahmad, I have the same exact problem. I am working in a patch that runs a FFT calculation and outputs signal:

SIGNAL FROM FILE~
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FFT~
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anything that converts it to a list
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unpack
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the rest of mu patch

However, I need to convert this signal output to a list of float numbers, so I will be able to read these numbers as input to the next step of the whole patch. Now, I am stuck in PD trying to do this conversion. Does anyone know how to solve it??
Thanks a lot!!