choose_proband: Choose a proband from the disease-affected relatives in a...
In SimRVPedigree: Simulate Pedigrees Ascertained for a Rare Disease

Choose a proband from the disease-affected relatives in a pedigree

1	choose_proband(ped_file, num_affected, ascertain_span, first_diagnosis)

`ped_file`	Pedigree simulated by `sim_ped`.
`num_affected`	Numeric vector. The minimum number of disease-affected relatives required for ascertainment.
`ascertain_span`	Numeric vector of length 2. The year span of the ascertainment period. This period represents the range of years during which the proband developed disease and the family would have been ascertained for multiple affected relatives.
`first_diagnosis`	Numeric. The first year that reliable diagnoses can be obtained regarding disease-affection status. By default, `first_diagnosis` `= NULL` so that all diagnoses are considered reliable. See details.