Extract a classic origin-destination migration flow matrix from a more detailed dis-aggregation of flows stored in an (`array`

).
Primarily intended to work with output from `ffs_demo`

.

`sum_od(x = NULL, zero_diag = TRUE, add_margins = TRUE)`

## Arguments

- x
Array of origin-destination matrices, where the first and second dimensions correspond to origin and destination respectively. Higher dimension(s) refer to additional migrant characteristic(s).

- zero_diag
Logical to indicate if to set diagonal terms to zero. Default `TRUE`

.

- add_margins
Logical to indicate if to add row and column for immigration and emigration totals. Default `TRUE`

## Value

Matrix from summing over the first and second dimension. Set diagonals to zero.

Returns a `matrix`

object of origin-destination flows