How to find most common elements of a list

Question

Given the following list    Jellicle    Cats    are    black    and    white     Jellicle    Cats      are    rather    small     Jellicle    Cats    are    merry    and      bright     And    pleasant    to    hear    when    they    caterwaul       Jellicle    Cats    have    cheerful    faces     Jellicle    Cats      have    bright    black    eyes     They    like    to    practise      their    airs    and    graces    And    wait    for    the    Jellicle      Moon    to    rise          I am trying to count how many times each word appears and display the top 3   However I am only looking to find the top three that have the first letter capitalized and ignore all words that do not have the first letter capitalized   I am sure there is a better way than this  but my idea was to do the following    put the first word in the list into another list called uniquewords delete the first word and all its duplicated from the original list add the new first word into unique words delete the first word and all its duplicated from original list  etc    until the original list is empty     count how many times each word in uniquewords appears in the original list find top 3 and print

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nltk is convenient for a lot of language processing stuff  It has methods for frequency distribution built in  Something like   import nltk fdist   nltk FreqDist your list    creates a frequency distribution from a list most common   fdist max        returns a single element top three   fdist keys    3    returns a list

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To just return a list containing the most common words   from collections import Counter words   i    love    you    i    you    a    are    you    you    fine    green   most common words   word for word  word count in Counter words  most common 3   print most common words   this prints     you    i    a     the 3 in  most common 3    specifies the number of items to print   Counter words  most common   returns a a list of tuples with each tuple having the word as the first member and the frequency as the second member The tuples are ordered by the frequency of the word    most common    item for item in Counter words  most common    print str most common      you   4     i   2     a   1     are   1     green   1     love  1     fine   1       the word for word  word counter in   extracts only the first member of the tuple

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The simple way of doing this would be  assuming your list is in  l      gt  gt  gt  counter       gt  gt  gt  for i in l  counter i    counter get i  0    1  gt  gt  gt  sorted    freq word  for word  freq in counter items      reverse True   3    6   Jellicle     5   Cats     3   to      Complete sample    gt  gt  gt  l     Jellicle    Cats    are    black    and    white     Jellicle    Cats    are    rather    small     Jellicle    Cats    are    merry    and    bright     And    pleasant    to    hear    when    they    caterwaul     Jellicle    Cats    have    cheerful    faces     Jellicle    Cats    have    bright    black    eyes     They    like    to    practise    their    airs    and    graces    And    wait    for    the    Jellicle    Moon    to    rise         gt  gt  gt  counter       gt  gt  gt  for i in l  counter i    counter get i  0    1       gt  gt  gt  counter   and   3      1   merry   1   rise    1   small    1   Moon   1   cheerful   1   bright   1   Cats   5   are   3   have   2   bright    1   for   1   their   1   rather   1   when   1   to   3   airs   1   black   2   They   1   practise   1   caterwaul    1   pleasant   1   hear   1   they   1   white    1   wait   1   And   2   like   1   Jellicle   6   eyes    1   the   1   faces    1   graces   1   gt  gt  gt  sorted    freq word  for word  freq in counter items      reverse True   3    6   Jellicle     5   Cats     3   to      With simple I mean working in nearly every version of python   if you don t understand some of the functions used in this sample  you can always do this in the interpreter  after pasting the code above     gt  gt  gt  help counter get   gt  gt  gt  help sorted

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The answer from  Mark Byers is best  but if you are on a version of Python  lt  2 7  but at least 2 5  which is pretty old these days   you can replicate the Counter class functionality very simply via defaultdict  otherwise  for python  lt  2 5  three extra lines of code are needed before d i    1  as in  Johnnysweb s answer    from collections import defaultdict class Counter        ITEMS          def   init   self  items           d   defaultdict int          for i in items              d i     1         self ITEMS   sorted d iteritems    reverse True  key lambda i  i 1       def most common self  n           return self ITEMS  n    Then  you use the class exactly as in Mark Byers s answer  i e    words to count    word for word in word list if word  1  isupper    c   Counter words to count  print c most common 3

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If you are using an earlier version of Python or you have a very good reason to roll your own word counter  I d like to hear it    you could try the following approach using a dict   Python 2 6 1  r261 67515  Feb 11 2010  00 51 29    GCC 4 2 1  Apple Inc  build 5646   on darwin Type  help    copyright    credits  or  license  for more information   gt  gt  gt  word list     Jellicle    Cats    are    black    and    white     Jellicle    Cats    are    rather    small     Jellicle    Cats    are    merry    and    bright     And    pleasant    to    hear    when    they    caterwaul     Jellicle    Cats    have    cheerful    faces     Jellicle    Cats    have    bright    black    eyes     They    like    to    practise    their    airs    and    graces    And    wait    for    the    Jellicle    Moon    to    rise         gt  gt  gt  word counter       gt  gt  gt  for word in word list          if word in word counter              word counter word     1         else              word counter word    1       gt  gt  gt  popular words   sorted word counter  key   word counter get  reverse   True   gt  gt  gt    gt  gt  gt  top 3   popular words  3   gt  gt  gt    gt  gt  gt  top 3   Jellicle    Cats    and     Top Tip  The interactive Python interpretor is your friend whenever you want to play with an algorithm like this  Just type it in and watch it go  inspecting elements along the way

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In Python 2 7 and above there is a class called Counter which can help you   from collections import Counter words to count    word for word in word list if word  1  isupper    c   Counter words to count  print c most common 3    Result      Jellicle   6     Cats   5     And   2          I am quite new to programming so please try and do it in the most barebones fashion    You could instead do this using a dictionary with the key being a word and the value being the count for that word  First iterate over the words adding them to the dictionary if they are not present  or else increasing the count for the word if it is present  Then to find the top three you can either use a simple O n log n   sorting algorithm and take the first three elements from the result  or you can use a O n  algorithm that scans the list once remembering only the top three elements   An important observation for beginners is that by using builtin classes that are designed for the purpose you can save yourself a lot of work and or get better performance  It is good to be familiar with the standard library and the features it offers

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A simple  two-line solution to this  which does not require any extra modules is the following code   lst     Jellicle    Cats    are    black    and   white            Jellicle    Cats   are    rather    small     Jellicle            Cats    are    merry    and   bright     And    pleasant               to   hear    when    they    caterwaul    Jellicle            Cats    have   cheerful    faces     Jellicle           Cats   have    bright    black   eyes     They    like           to    practise   their    airs    and    graces    And            wait    for    the    Jellicle   Moon    to    rise         lst sorted sorted  ss for ss in set lst  if len ss  gt 0 and ss istitle                         key lst count                      reverse True  print lst sorted 0 3    Output     Jellicle    Cats    And     The term in squared brackets returns all unique strings in the list  which are not empty and start with a capital letter  The sorted   function then sorts them by how often they appear in the list  by using the lst count key  in reverse order

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There s two standard library ways to find the most frequent value in a list   statistics mode   from statistics import mode most common   mode  3  2  2  2  1  1      2 most common   mode  3  2      StatisticsError  no unique mode    Raises an exception if there s no unique most frequent value Only returns single most frequent value   collections Counter most common   from collections import Counter most common  count   Counter  3  2  2  2  1  1   most common 2     2  3  most common 1  count 1    most common 2  count 2    Counter  3  2  2   most common 2      2  2    3  1     Can return multiple most frequent values Returns element count as well   So in the case of the question  the second one would be the right choice  As a side note  both are identical in terms of performance

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Is t it just this       word list   Jellicle    Cats    are    black    and    white     Jellicle    Cats      are    rather    small     Jellicle    Cats    are    merry    and      bright     And    pleasant    to    hear    when    they    caterwaul       Jellicle    Cats    have    cheerful    faces     Jellicle    Cats      have    bright    black    eyes     They    like    to    practise      their    airs    and    graces    And    wait    for    the    Jellicle      Moon    to    rise          from collections import Counter c   Counter word list  c most common 3    Which should output      Jellicle   6     Cats   5     are   3

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If you are using Count  or have created your own Count-style dict and want to show the name of the item and the count of it  you can iterate around the dictionary like so   top 10 words   Counter my long list of words    Iterate around the dictionary for word in top 10 words            print the word         print word 0            print the count         print word 1    or to iterate through this in a template      for word in top 10 words             lt p gt Word     word 0    lt  p gt           lt p gt Count     word 1    lt  p gt     endfor      Hope this helps someone

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I will like to answer this with numpy  great powerful array computation module in python   Here is code snippet    import numpy a     Jellicle    Cats    are    black    and    white     Jellicle    Cats      are    rather    small     Jellicle    Cats    are    merry    and      bright     And    pleasant    to    hear    when    they    caterwaul       Jellicle    Cats    have    cheerful    faces     Jellicle    Cats      have    bright    black    eyes     They    like    to    practise      their    airs    and    graces    And    wait    for    the    Jellicle      Moon    to    rise        dict zip  numpy unique a  return counts True      Output       1   And   2   Cats   5   Jellicle   6   Moon   1   They   1   airs   1   and   3   are   3   black   2   bright   1   bright    1   caterwaul    1   cheerful   1   eyes    1   faces    1   for   1   graces   1   have   2   hear   1   like   1   merry   1   pleasant   1   practise   1   rather   1   rise    1   small    1   the   1   their   1   they   1   to   3   wait   1   when   1   white    1    Output is in dictionary object in format of  key  value  pairs  where value is count of particular word  This answer is inspire by another answer on stackoverflow  you can view it here

[python] How to find most common elements of a list?

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