At `at`¶

Returns the element at the specified index or key from a collection.

Syntax¶

(at collection index)
(at collection 'key)

Examples¶

Vector/List Indexing¶

↪ (at [1 2 3 4 5] 2)
3

↪ (at [10 20 30] 0)
10

↪ (at (list "Alice" "Bob" "Charlie") 1)
"Bob"

Dictionary Access¶

↪ (set d (dict [a b c] [1 2 3]))
↪ (at d 'b)
2

↪ (at (dict [x y] [100 200]) 'y)
200

Table Column Access¶

↪ (set at_t (table [name age] (list (list "Alice" "Bob") [25 30])))

↪ (at at_t 'name)
(
  Alice
  Bob
)

↪ (at at_t 'age)
[25 30]

Reserved Word Columns (CRITICAL)¶

When a table column name matches a RayFall built-in function (like timestamp, type, count), you MUST use (at table 'column) to access it:

;; Create table with 'timestamp' column (reserved word)
↪ (set trades (table [timestamp price amount] (list [1000 2000 3000] [100.5 101.0 99.5] [10 20 15])))

;; WRONG - timestamp is a built-in function
;; (select {ts: timestamp from: trades})  ;; ERROR!

;; CORRECT - use at with quoted symbol
↪ (select {ts: (at trades 'timestamp) from: trades})

Reserved Word Columns

The following column names conflict with built-in functions and require (at table 'column) syntax:

timestamp - temporal function
type - type inspection
count - counting function
date, time - temporal functions
first, last - item access
sum, avg, min, max - aggregations
key, value - dictionary access
where, group - query clauses
distinct, reverse - collection operations

Parameters

collection: Vector, list, dictionary, or table
index/key: Integer index (0-based) or quoted symbol for key access

Tip

Use at for: - Accessing elements by position in vectors/lists - Looking up values by key in dictionaries - Extracting columns from tables, especially reserved-word columns

At at¶