Filtering

Coral.Frame.filter(frame, mask) keeps the rows marked true by a tensor[n, bool] mask. The mask must have the frame's row count. The result has one row for each true entry, in its original order.

Chelis does not compare a tensor with a scalar by implicit broadcasting. For a scalar threshold, map a predicate over the column values and convert the booleans to a tensor:

module Coral.BookFilter
import Coral.Frame (FloatCol, from_pairs, filter, get_float_col, nrows)
export (main)
def main() -> i64 = {
  frame = from_pairs([("price", FloatCol(to_tensor([10.0f32, 80.0f32, 100.0f32])))])
  mask = to_tensor(map(fn (price: f32) -> gt(price, 75.0f32), to_list(get_float_col(frame, "price"))))
  kept = filter(frame, mask)
  nrows(kept)
}

main returns 2. To compare two tensor columns directly, their shapes and dtypes must match; see the Chelis operation reference.

The checker rejects a mask whose length differs from the frame's row count, reporting dimension mismatch: Lit(2) vs Lit(3) for a two-entry mask on a three-row frame. An all-false mask returns a frame with the same columns and zero rows.

Select rows by position

Function	Signature	Rows kept
head	(df: Frame[n], count: i64) -> Frame[k]	The first count rows
tail	(df: Frame[n], count: i64) -> Frame[k]	The last count rows
slice	(df: Frame[n], start: i64, finish: i64) -> Frame[k]	Rows start up to but not including finish

Counts and bounds are clamped rather than rejected. A negative count keeps no rows; a count larger than the frame keeps every row. slice clamps start to 0 and finish to the row count, and returns zero rows when finish <= start. On a five-row frame, head(f, 10) keeps all five rows, head(f, -1) and slice(f, 3, 1) keep none, and slice(f, 1, 3) keeps rows 1 and 2.

Sort rows

sort_by(df: Frame[n], name: string, ascending: bool) -> Frame[n] reorders every column by the values in column name. A missing name fails with sort_by: column not found.

• Order. An ascending sort keeps equal keys in their input order. ascending = false reverses the whole ascending result, so equal keys appear in reverse input order.
• NaN. Float NaNs sort after every number when ascending, and first when descending. Sorting [3.0, NaN, 1.0, 2.0, 1.0] ascending gives [1.0, 1.0, 2.0, 3.0, NaN].
• Integer masks. A masked integer sorts by its stored number, usually 0, not as a missing value.
• Bool. false sorts before true.
• Strings. Strings compare character by character with Coral's own ranking, not Unicode code points: lowercase a to z, then uppercase A to Z, then digits 0 to 9, then _ - . space % / : + * # @. Every other character ranks after those and equal to the others. A prefix sorts before a longer string. Sorting ["b", "B", "a", "ab", "b", ""] ascending gives ["", "a", "ab", "b", "b", "B"].