Finding the mode of a list

Question

Given a list of items  recall that the mode of the list is the item that occurs most often   I would like to know how to create a function that can find the mode of a list but that displays a message if the list does not have a mode  e g   all the items in the list only appear once   I want to make this function without importing any functions  I m trying to make my own function from scratch

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In case you are interested in either the smallest  largest or all modes   def get small mode numbers  out mode       counts    k numbers count k  for k in set numbers       modes   sorted dict filter lambda x  x 1     max counts values     counts items     keys        if out mode   smallest           return modes 0      elif out mode   largest           return modes -1      else          return modes

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Perhaps try the following   It is O n  and returns a list of floats  or ints    It is thoroughly  automatically tested   It uses collections defaultdict  but I d like to think you re not opposed to using that   It can also be found at https   stromberg dnsalias org  strombrg stddev html def compute mode list   typing List float   - gt  typing List float        quot  quot  quot                             Compute the mode of list        Note that the return value is a list  because sometimes there is a tie for  quot most common value quot                                                                                See https   stackoverflow com questions 10797819 finding-the-mode-of-a-list      quot  quot  quot                                                                                                              if not list           raise ValueError  Empty list       if len list      1                     raise ValueError  Single-element list       value to count dict  typing DefaultDict float  int    collections defaultdict int      for element in list           value to count dict element     1     count to values dict   collections defaultdict list      for value  count in value to count dict items               count to values dict count  append value                                 counts   list count to values dict      if len counts     1                                                                                      raise ValueError  All elements in list are the same                 maximum occurrence count   max counts      if maximum occurrence count    1          raise ValueError  No element occurs more than once       minimum occurrence count   min counts      if maximum occurrence count  lt   minimum occurrence count          raise ValueError  Maximum count not greater than minimum count       return count to values dict maximum occurrence count

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def mode data       lst         hgh 0     for i in range len data            lst append data count data i        m  max lst      ml    x for x in data if data count x   m    to find most frequent values     mode          for x in ml   to remove duplicates of mode         if x not in mode          mode append x      return mode print mode  1 2 2 2 2 7 7 5 5 5 5

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You can use the Counter supplied in the collections package which has a mode-esque function  from collections import Counter data   Counter your list in here  data most common       Returns all unique items and their counts data most common 1     Returns the highest occurring item   Note  Counter is new in python 2 7 and is not available in earlier versions

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import numpy as np def get mode xs       values  counts   np unique xs  return counts True      max count index   np argmax counts   return the index with max value counts     return values max count index  print get mode  1 7 2 5 3 3 8 3 2

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A little longer  but can have multiple modes and can get string with most counts or mix of datatypes    def getmode inplist          with list of items as input  returns mode             dictofcounts          listofcounts          for i in inplist          countofi   inplist count i    count items for each item in list         listofcounts append countofi    add counts to list         dictofcounts i  countofi   add counts and item in dict to get later     maxcount   max listofcounts    get max count of items     if maxcount   1          print  There is no mode for this dataset  values occur only once      else          modelist        if more than one mode  add to list to print out         for key  item in dictofcounts iteritems                if item   maxcount    get item from original list with most counts                 modelist append str key           print  The mode s  are     and   join modelist          return modelist

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Mode of a data set is are the member s  that occur s  most frequently in the set  If there are two members that appear most often with same number of times  then the data has two modes  This is called bimodal If there are more than 2 modes  then the data would be called multimodal  If all the members in the data set appear the same number of times  then the data set has no mode at all  Following function modes   can work to find mode s  in a given list of data  import numpy as np  import pandas as pd  def modes arr       df   pd DataFrame arr  columns   Values        dat   pd crosstab df  Values    columns   Freq        if len np unique  dat  Freq       gt  1          mode   list dat index np array dat  Freq      max dat  Freq               return mode     else          print  quot There is NO mode in the data set quot    Output    For a list of numbers in x as In  1   x    2  3  4  5  7  9  8  12  2  1  1  1  3  3  2  6  12  3  7  8  9  7  12  10  10  11  12  2  In  2   modes x  Out 2    2  3  12    For a list of repeated numbers in y as In  3   y    2  2  3  3  4  4  10  10  In  4   modes y  Out 4   There is NO mode in the data set   For a list of strings characters in z as In  5   z     a    b    b    b    e    e    e    d    g    g    c    g    g    a    a    c    a   In  6   modes z  Out 6     a    g    If we do not want to import numpy or pandas to call any function from these packages  then to get this same output  modes   function can be written as  def modes arr       cnt          for i in arr          cnt append arr count i       uniq cnt          for i in cnt          if i not in uniq cnt              uniq cnt append i      if len uniq cnt   gt  1          m              for i in list range len cnt                 if cnt i     max uniq cnt                   m append arr i           mode              for i in m              if i not in mode                  mode append i          return mode     else          print  quot There is NO mode in the data set quot

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You can use the max function and a key  Have a look at python max function using  key  and lambda expression   max set lst   key lst count

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There are many simple ways to find the mode of a list in Python such as   import statistics statistics mode  1 2 3 3    gt  gt  gt  3   Or  you could find the max by its count  max array  key   array count    The problem with those two methods are that they don t work with multiple modes  The first returns an error  while the second returns the first mode    In order to find the modes of a set  you could use this function   def mode array       most   max list map array count  array        return list set filter lambda x  array count x     most  array

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Why not just  def print mode  thelist     counts        for item in thelist      counts  item    counts get  item  0    1   maxcount   0   maxitem   None   for k  v in counts items         if v  gt  maxcount        maxitem   k       maxcount   v   if maxcount    1      print  All values only appear once    elif counts values   count  maxcount   gt  1      print  List has multiple modes    else      print  Mode of list    maxitem   This doesn t have a few error checks that it should have  but it will find the mode without importing any functions and will print a message if all values appear only once   It will also detect multiple items sharing the same maximum count  although it wasn t clear if you wanted that

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Python 3 4 includes the method statistics mode  so it is straightforward    gt  gt  gt  from statistics import mode  gt  gt  gt  mode  1  1  2  3  3  3  3  4    3   You can have any type of elements in the list  not just numeric    gt  gt  gt  mode   red    blue    blue    red    green    red    red      red

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function to find mode def mode data         modecnt 0  for count of number appearing     for i in range len data            icount data count data i    for storing count of each number in list will be stored         if icount gt modecnt   the loop activates if current count if greater than the previous count              mode data i   here the mode of number is stored              modecnt icount  count of the appearance of number is stored     return mode print mode data1

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If you want a clear approach  useful for classroom and only using lists and dictionaries by comprehension  you can do   def mode my list         Form a new list with the unique elements     unique list   sorted list set my list          Create a comprehensive dictionary with the uniques and their count     appearance    a my list count a  for a in unique list         Calculate max number of appearances     max app   max appearance values          Return the elements of the dictionary that appear that   of times     return  k  v for k  v in appearance items   if v    max app

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Here is a simple function that gets the first mode that occurs in a list  It makes a dictionary with the list elements as keys and number of occurrences and then reads the dict values to get the mode   def findMode readList       numCount        highestNum 0     for i in readList          if i in numCount keys    numCount i     1         else  numCount i    1     for i in numCount keys            if numCount i   gt  highestNum              highestNum numCount i              mode i     if highestNum    1  print mode      elif highestNum    1  print  All elements of list appear once

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Simple code that finds the mode of the list without any imports    nums    your list goes here nums sort   counts   dict   for i in nums      counts i    counts get i  0    1 mode   max counts  key counts get    In case of multiple modes  it should return the minimum node

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This function returns the mode or modes of a function no matter how many  as well as the frequency of the mode or modes in the dataset  If there is no mode  ie  all items occur only once   the function returns an error string  This is similar to A nagpal s function above but is  in my humble opinion  more complete  and I think it s easier to understand for any Python novices  such as yours truly  reading this question to understand    def l mode list in       count dict          for e in  list in              count   list in count e          if e not in count dict keys                count dict e    count     max count   0      for key in count dict           if count dict key   gt   max count              max count   count dict key      corr keys           for corr key  count value in count dict items            if count dict corr key     max count              corr keys append corr key      if max count    1 and len count dict     1           return  There is no mode for this data set  All values occur only once       else           corr keys   sorted corr keys          return corr keys  max count

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This will return all modes   def mode numbers      largestCount   0     modes          for x in numbers          if x in modes              continue         count   numbers count x          if count  gt  largestCount              del modes                modes append x              largestCount   count         elif count    largestCount              modes append x      return modes

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Extending the Community answer that will not work when the list is empty  here is working code for mode   def mode arr           if arr                  return None         else              return max set arr   key arr count

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Short  but somehow ugly   def mode arr        m   max  arr count a  for a in arr       return  x for x in arr if arr count x     m  0  if m gt 1 else None   Using a dictionary  slightly less ugly   def mode arr        f          for a in arr   f a    f get a 0  1     m   max f values        t     x f x   for x in f if f x   m      return m  gt  1 t 0  0  else None

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Taking a leaf from some statistics software  namely SciPy and MATLAB  these just return the smallest most common value  so if two values occur equally often  the smallest of these are returned  Hopefully an example will help    gt  gt  gt  from scipy stats import mode   gt  gt  gt  mode  1  2  3  4  5    array   1     array   1       gt  gt  gt  mode  1  2  2  3  3  4  5    array   2     array   2       gt  gt  gt  mode  1  2  2  -3  -3  4  5    array  -3     array   2       Is there any reason why you can  t follow this convention

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For a number to be a mode  it must occur more number of times than at least one other number in the list  and it must not be the only number in the list  So  I refactored  mathwizurd s answer  to use the difference method  as follows    def mode array               returns a set containing valid modes     returns a message if no valid mode exists       - when all numbers occur the same number of times       - when only one number occurs in the list        - when no number occurs in the list              most   max map array count  array   if array else None     mset   set filter lambda x  array count x     most  array       return mset if set array  - mset else  list does not have a mode      These tests pass successfully    mode        None  mode  1      None mode  1  1      None  mode  1  1  2  2      None

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For those looking for the minimum mode  e g case of bi-modal distribution  using numpy   import numpy as np mode   np argmax np bincount your list

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def mode inp list       sort list   sorted inp list      dict1          for i in sort list                      count   sort list count i              if i not in dict1 keys                    dict1 i    count      maximum   0  no  of occurences     max key   -1  element having the most occurences      for key in dict1          if dict1 key  gt maximum               maximum   dict1 key              max key   key          elif dict1 key   maximum               if key lt max key                   maximum   dict1 key                  max key   key      return max key

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I wrote up this handy function to find the mode     def mode nums       corresponding        occurances        for i in nums              count   nums count i              corresponding update  i count        for i in corresponding              freq corresponding i              occurances append freq       maxFreq max occurances       keys corresponding keys       values corresponding values        index v   values index maxFreq      global mode     mode   keys index v      return mode

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Here is how you can find mean median and mode of a list   import numpy as np from scipy import stats   to take input size   int input    numbers   list map int  input   split      print np mean numbers   print np median numbers   print int stats mode numbers  0

[python] Finding the mode of a list

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