option to prevent the aggregation of age groups (in case of sparse data)

[lwillem]

The current implementation of contact_matrix() aggregates the oldest age groups, for example, combining the 60-89 and 90+ age groups into a single "60+" category if there is no data for the 90+ group. More specifically:

---

#line 275
adjust age.group.brakes to the lower and upper ages in the survey
survey$participants[, lower.age.limit := reduce_agegroups(
get(columns[["participant.age"]]),
age.limits[age.limits < max.age]
)]
part.age.group.breaks <- c(age.limits[age.limits < max.age], max.age)
part.age.group.present <- age.limits[age.limits < max.age]

---

Would it be useful to include a flag to disable this behavior and instead return a matrix with NA values if needed, while keeping the age groups fixed? This would be helpful in cases where post-processing assumes a matrix with a fixed number of columns (N), as receiving one with N-1 columns could cause issues.

[sbfnk]

Yes, and I think perhaps your suggested behaviour would actually make sense as default.