Which data set option controls the number of observations read from an input data set?

The OBS= data set option is specifically designed to control the number of observations that are read from an input data set. By using this option, you can specify the maximum number of observations that should be processed, which allows for selective data manipulation or analysis without needing to modify the original data set directly.

For instance, if you have a large dataset but are only interested in the first 100 observations for a certain analysis, applying the OBS= option with a value of 100 would achieve that goal. This functionality is particularly useful for efficiency when working with large datasets, enabling users to limit the data being read into memory and processed accordingly.

In contrast, the FIRSTOBS= option specifies the starting observation to read from the dataset, thereby controlling where the reading starts but not the total number of observations accessed. The WHERE= option is used for filtering observations based on specific conditions, while the DROP= option relates to excluding specific variables from the dataset, not the number of observations read. Each of these options serves different purposes, but OBS= is the definitive choice for limiting the observations processed from a dataset.