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Note that fmap, join, append and bind are well-defined, since they're applied to progressively deeper arguments at each recursive call. The list type is an additive monad, with nil as the monadic zero and append as monadic sum. Lists form a monoid under the append operation. The identity element of the monoid is the empty list, nil.
[4]: 114 A DataFrame is a 2-dimensional data structure of rows and columns, similar to a spreadsheet, and analogous to a Python dictionary mapping column names (keys) to Series (values), with each Series sharing an index. [4]: 115 DataFrames can be concatenated together or "merged" on columns or indices in a manner similar to joins in SQL.
Suppose that "L" is a variable pointing to the last node of a circular linked list (or null if the list is empty). To append "newNode" to the end of the list, one may do insertAfter(L, newNode) L := newNode To insert "newNode" at the beginning of the list, one may do insertAfter(L, newNode) if L = null L := newNode
Following Lisp, other high-level programming languages which feature linked lists as primitive data structures have adopted an append. To append lists, as an operator, Haskell uses ++, OCaml uses @. Other languages use the + or ++ symbols to nondestructively concatenate a string, list, or array.
The prototypical append-only data structure is the log file. Log-structured data structures found in Log-structured file systems and databases work in a similar way: every change (transaction) that happens to the data is logged by the program, and on retrieval the program must combine the pieces of data found in this log file. [ 9 ]
Empty constructs an empty list, Cons(x, L) constructs a list by prepending or concatenating value x in front of list L. A list such as [1, 2, 3] is therefore the declaration Cons(1, Cons(2, Cons(3, Empty))). It is possible to describe the location in such a list as the number of steps from the front of the list to the target location.
If this was just five years ago, let alone 10 or 20, the prospect of 72-year-old Bill Belichick as a college football coach would have been more about a splashy hire than the promise of great success.
Gary Kessler's list of file signatures; Online File Signature Database for Forensic Practitioners, a private compilation free to Law Enforcement; Man page for compress, uncompress, and zcat on SCO Open Server; Public Database of File Signatures [dead link ] Complete list of magic numbers with sample files