Returns the number of observations that are used by an initialized model. If there are missing values, the number of used observations may differ from the numbers of observations of the data set that was passed to the model's initialization.

## Examples

```
# \donttest{
model <- new(
"diseq_basic", # model type
subject = ID, time = TREND, quantity = HS, price = RM,
demand = RM + TREND + W + CSHS + L1RM + L2RM + MONTH,
supply = RM + TREND + W + L1RM + MA6DSF + MA3DHF + MONTH,
fair_houses()
)
# get the number observations
nobs(model)
#> [1] 130
# }
```