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0.1
Python lists have a built-in
list.sort()
method that modifies the listin-place. There is also a sorted()
built-in function that builds a newsorted list from an iterable.In this document, we explore the various techniques for sorting data using Python.
Sorting Basics¶
A simple ascending sort is very easy: just call the
sorted()
function. Itreturns a new sorted list:You can also use the
list.sort()
method. It modifies the listin-place (and returns None
to avoid confusion). Usually it’s less convenientthan sorted()
- but if you don’t need the original list, it’s slightlymore efficient.Another difference is that the
list.sort()
method is only defined forlists. In contrast, the sorted()
function accepts any iterable.![One One](https://upload.wikimedia.org/wikipedia/commons/thumb/8/86/Emeryson_F2_F1.jpg/1200px-Emeryson_F2_F1.jpg)
Key Functions¶
Both
list.sort()
and sorted()
have a key parameter to specify afunction (or other callable) to be called on each list element prior to makingcomparisons.For example, here’s a case-insensitive string comparison:
The value of the key parameter should be a function (or other callable) thattakes a single argument and returns a key to use for sorting purposes. Thistechnique is fast because the key function is called exactly once for eachinput record.
A common pattern is to sort complex objects using some of the object’s indicesas keys. For example:
The same technique works for objects with named attributes. For example:
Operator Module Functions¶
The key-function patterns shown above are very common, so Python providesconvenience functions to make accessor functions easier and faster. The
operator
module has itemgetter()
,attrgetter()
, and a methodcaller()
function.Using those functions, the above examples become simpler and faster:
Commander 3 8 0 9. The operator module functions allow multiple levels of sorting. For example, tosort by grade then by age:
Ascending and Descending¶
Both
list.sort()
and sorted()
accept a reverse parameter with aboolean value. This is used to flag descending sorts. For example, to get thestudent data in reverse age order:Sort Stability and Complex Sorts¶
Sorts are guaranteed to be stable. That means thatwhen multiple records have the same key, their original order is preserved.
Notice how the two records for blue retain their original order so that
('blue',1)
is guaranteed to precede ('blue',2)
.This wonderful property lets you build complex sorts in a series of sortingsteps. For example, to sort the student data by descending grade and thenascending age, do the age sort first and then sort again using grade:
This can be abstracted out into a wrapper function that can take a list andtuples of field and order to sort them on multiple passes.
The Timsort algorithm used in Pythondoes multiple sorts efficiently because it can take advantage of any orderingalready present in a dataset.
The Old Way Using Decorate-Sort-Undecorate¶
This idiom is called Decorate-Sort-Undecorate after its three steps:
- First, the initial list is decorated with new values that control the sort order.
- Second, the decorated list is sorted.
- Finally, the decorations are removed, creating a list that contains only theinitial values in the new order.
Flux 4 1 11 – advanced web design tool. For example, to sort the student data by grade using the DSU approach:
This idiom works because tuples are compared lexicographically; the first itemsare compared; if they are the same then the second items are compared, and soon.
It is not strictly necessary in all cases to include the index i in thedecorated list, but including it gives two benefits:
- The sort is stable – if two items have the same key, their order will bepreserved in the sorted list.
- The original items do not have to be comparable because the ordering of thedecorated tuples will be determined by at most the first two items. So forexample the original list could contain complex numbers which cannot be sorteddirectly.
Another name for this idiom isSchwartzian transform,after Randal L. Schwartz, who popularized it among Perl programmers.
Now that Python sorting provides key-functions, this technique is not often needed.
The Old Way Using the cmp Parameter¶
Many constructs given in this HOWTO assume Python 2.4 or later. Before that,there was no
sorted()
builtin and list.sort()
took no keywordarguments. Instead, all of the Py2.x versions supported a cmp parameter tohandle user specified comparison functions.In Py3.0, the cmp parameter was removed entirely (as part of a larger effort tosimplify and unify the language, eliminating the conflict between richcomparisons and the
__cmp__()
magic method).In Py2.x, sort allowed an optional function which can be called for doing thecomparisons. That function should take two arguments to be compared and thenreturn a negative value for less-than, return zero if they are equal, or returna positive value for greater-than. For example, we can do:
Or you can reverse the order of comparison with:
When porting code from Python 2.x to 3.x, the situation can arise when you havethe user supplying a comparison function and you need to convert that to a keyfunction. The following wrapper makes that easy to do:
To convert to a key function, just wrap the old comparison function:
In Python 3.2, the
functools.cmp_to_key()
function was added to thefunctools
module in the standard library.Odd and Ends¶
- For locale aware sorting, use
locale.strxfrm()
for a key function orlocale.strcoll()
for a comparison function. - The reverse parameter still maintains sort stability (so that records withequal keys retain the original order). Quiver take better notes 3 1 2. Interestingly, that effect can besimulated without the parameter by using the builtin
reversed()
functiontwice: - The sort routines are guaranteed to use
__lt__()
when making comparisonsbetween two objects. So, it is easy to add a standard sort order to a class bydefining an__lt__()
method: - Key functions need not depend directly on the objects being sorted. A keyfunction can also access external resources. For instance, if the student gradesare stored in a dictionary, they can be used to sort a separate list of studentnames:
(Redirected from Key 2)
City | Castlefield |
---|---|
Broadcast area | Greater Manchester |
Frequency | MW: 1152 kHz DAB: 11C |
Slogan | The Good Times Sound Like This |
Programming | |
Format | Classic Hits |
Ownership | |
Owner | Bauer |
Hits Radio Manchester Greatest Hits Radio North West Greatest Hits Radio UK Hits Radio UK | |
History | |
First air date | 2 April 1974 |
Technical information | |
53°29′28″N2°06′52″W / 53.49124°N 2.11445°WCoordinates: 53°29′28″N2°06′52″W / 53.49124°N 2.11445°W |
Greatest Hits Radio Greater Manchester is an Independent local radio station owned and operated by Bauer as part of the Greatest Hits Radio network. It forms part of Greatest Hits Radio North West
History[edit]
Early years[edit]
The station began broadcasting at 5am on Tuesday 2 April 1974 as Piccadilly Radio on 261 m (1151 kHz then) AM/MW and on 97.0 MHz FM (from the same transmitter in Saddleworth that is now used by Hits Radio Manchester). The station was named after Piccadilly Gardens in Manchester, and Piccadilly Plaza was home to the station's first studios until 1996, when Piccadilly 1152 and Hits Radio were relocated to the Castlefield area of Manchester.
Piccadilly's founding managing director was Philip Birch, who previously ran the highly influential pirate station Radio London until it closed down ahead of the Marine Offences Act in August 1967. The first presenter on air was Roger Day – himself an ex-pirate radio presenter – and the first song played on air was Good Vibrations by The Beach Boys.
Many of Britain's best-known broadcasters started their careers at Piccadilly, including Chris Evans, Mike Sweeney, Steve Penk, James H Reeve, Andy Peebles, Gary Davies, Tim Grundy, Timmy Mallett, Pete Mitchell, Geoff Lloyd, Mark Radcliffe, James Stannage, Stu Allan, Nick Robinson and Karl Pilkington.
Journalist Paul Lockitt joined Piccadilly in 1979 and became the station's longest serving on-air employee, working as a producer, presenter and newscaster until his departure in 2017.
One Key 2 0 6 X 2
FM/MW split[edit]
Piccadilly Radio split into two services in 1988, with Key 103 broadcast on FM with a contemporary music format, while Piccadilly continued on AM, initially under its full service format, gradually adopting a 'golden oldies' music playlist as Piccadilly Gold.
In the mid-1990s, Piccadilly Gold became Piccadilly 1152 as the playlist moved away from 'golden oldies' to a mix of classic and current easy-listening music. The late-night phone-in with James Stannage became the most popular radio talk show outside London, whilst the Dave Ward and Umberto breakfast show helped the station to become one of the biggest AM stations.
In 1994, a rival station, Fortune 1458 (later renamed 1458 Lite AM, today broadcasting as 1458 Capital Gold) commenced on BBC GMR's former AM frequency. Despite heavy marketing, and many ex-Piccadilly presenters on the new station, Piccadilly 1152 remained Manchester's most popular station, other than sister station Key 103, until the late 1990s when smaller, localised FM stations in Oldham, Warrington and Bury began to erode away Piccadilly's audience base.
Magic 1152[edit]
In 1994, Piccadilly (Key 103/Piccadilly 1152) were part of the Transworld Radio Group, which was bought by present owners Bauer Radio (then EMAP). In 1999/2000, parent company EMAP re-branded the station as Magic 1152, to fall in-line with the other nine Magic stations they owned across London and the north of England.
One Key 2 0 6 0
The idea of a 'Magic brand' of stations was seen to be beneficial when selling air time to national advertisers. This change in name also coincided with the 25th birthday of Piccadilly Radio. The station was branded as 'Piccadilly 1152 – the magic of Manchester' during the transition. Except for a short spell in 2000 – when Key 103 was briefly renamed Piccadilly Key 103 – the Piccadilly brand was finally retired.
In December 2001, EMAP decided that it was more economical for the Magic network to share off-peak programmes. Magic 1152, in line with the other seven Magic AM stations in northern England, began networking 10am – 2pm, and 7pm – 6am by carrying programming from Magic 105.4 in London. During these hours, it was simply known as Magic, although there were local commercial breaks, and local news on the hour.
In January 2003, after a sharp decline in listening, the station ceased networking with the London station, and a regional northern network was created with the Manchester station providing networked output at weekends while sister station Magic 1152 in Newcastle provided weekday programming.
From July 2006, more networking was introduced across the Northern Magic AM network, with local output reduced to a daily four-hour breakfast show, local news and advertising. In April 2012, Magic 1152, inline with the majority of other Magic North stations, dropped local weekend breakfast shows.
Between March 2013 and December 2014, weekday breakfast was syndicated with Magic 1548 in Liverpool and Magic 999 in Preston.[1]
Key 2/Key Radio[edit]
One Key 2 0 6 X 4
On 5 January 2015, Magic 1152 was rebranded as Key 2, as Magic FM in London went national on DAB. The station formed part of the Bauer City 2 network. All programming was now networked with the other Bauer AM stations in the North although local news, weather and travel continue to be broadcast as opt-outs during the day.
In June 2018, following the relaunch and rebrand of Key 103 as Hits Radio, the station was rebranded again as Key Radio, retaining the former local identity in a secondary capacity.[2]
Greatest Hits Radio[edit]
On 7 January 2019, Key Radio rebranded as Greatest Hits Manchester.[3]
References[edit]
- ^Magic AM starts networking at breakfast Radio Today, 15 February 2013
- ^Key 2 on AM and DAB rebrands as Key Radio, Radio Today, 4 June 2018
- ^Bauer Media to launch Greatest Hits Radio network Radio Today, 15 November 2018
External links[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Greatest_Hits_Radio_Greater_Manchester&oldid=977373268'