The modeling of out-of-equilibrium many-body quantum systems requires to go beyond low-energy physics
and single or few bodies densities of states. Many-body localization, presence or lack of thermalization
and quantum chaos are examples of phenomena in which states at different energy scales, including highly excited
ones, contribute to dynamics and therefore affect the system's properties. Quantifying these contributions requires
the Many-Body Density of States (MBDoS), a function whose calculation becomes challenging even for non-interacting
identical particles due to the difficulty to enumerate accessible states while enforcing the exchange
symmetry. In the present work, we introduce a new approach to evaluate the MBDoS in the general case of non-interacting systems of identical quantum particles. The starting point of our method is the principal component analysis of a filling matrix $F$ describing
how $N$ particles can be distributed into $L$ single-particle energy levels. We show that
the many body spectrum can be expanded as a weighted sum of singular vectors of the filling matrix.
The weighting coefficients only involve renormalized energies obtained from the single body spectrum.
We illustrate our method in two classes of problems that are mapped into spinless fermions:
(i) non-interacting electrons in a homogeneous tight-binding model in 1D and 2D,
and (ii) interacting spins in a chain under a transverse field.