1.7.6 Counting and averaging by destination🔗ℹ

(define grouped-data

(group-count (table-groupby (table-cut subset '(dest dep_delay)) '(dest))))

> (define by-dest     (~> subset         (group-by "dest")         (agg (alias (count "dep_delay") "departed")              (alias (mean "dep_delay") "mean_delay"))         (sort "dest")))

> by-dest

shape: (96, 3) ┌──────┬──────────┬────────────┐ │ dest ┆ departed ┆ mean_delay │ │ ---  ┆ ---      ┆ ---        │ │ str  ┆ u32      ┆ f64        │ ╞══════╪══════════╪════════════╡ │ ABQ  ┆ 4        ┆ -3.0       │ │ ACK  ┆ 4        ┆ 9.25       │ │ ALB  ┆ 8        ┆ 20.375     │ │ ATL  ┆ 271      ┆ 15.254613  │ │ AUS  ┆ 41       ┆ 13.439024  │ │ …    ┆ …        ┆ …          │ │ SYR  ┆ 28       ┆ 42.714286  │ │ TPA  ┆ 120      ┆ 13.141667  │ │ TUL  ┆ 6        ┆ 8.5        │ │ TYS  ┆ 8        ┆ 8.125      │ │ XNA  ┆ 17       ┆ 2.882353   │ └──────┴──────────┴────────────┘

count, like group-count, skips missing values: on the full file ATL has 16,898, the post’s figure, of 17,215 flights, and a mean delay of 12.5 minutes. The groups come back in no fixed order, as in Python; sort them to print.