Count the number occurrences of a character in a string

Question

What s the simplest way to count the number of occurrences of a character in a string   e g  count the number of times  a  appears in  Mary had a little lamb

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I am a fan of the pandas library  in particular the value counts   method  You could use it to count the occurrence of each character in your string    gt  gt  gt  import pandas as pd  gt  gt  gt  phrase    I love the pandas library and its  value counts    method   gt  gt  gt  pd Series list phrase   value counts        8 a    5 e    4 t    4 o    3 n    3 s    3 d    3 l    3 u    2 i    2 r    2 v    2      2 h    2 p    1 b    1 I    1 m    1      1 y    1      1      1 c    1 dtype  int64

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str count a  is the best solution to count a single character in a string  But if you need to count more characters you would have to read the whole string as many times as characters you want to count   A better approach for this job would be   from collections import defaultdict  text    Mary had a little lamb  chars   defaultdict int   for char in text      chars char     1   So you ll have a dict that returns the number of occurrences of every letter in the string and 0 if it isn t present    gt  gt  gt chars  a   4  gt  gt  gt chars  x   0     For a case insensitive counter you could override the mutator and accessor methods by subclassing defaultdict  base class  ones are read-only    class CICounter defaultdict       def   getitem   self  k           return super     getitem   k lower         def   setitem   self  k  v           super     setitem   k lower    v    chars   CICounter int   for char in text      chars char     1   gt  gt  gt chars  a   4  gt  gt  gt chars  M   2  gt  gt  gt chars  x   0

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Regular expressions are very useful if you want case-insensitivity  and of course all the power of regex    my string    Mary had a little lamb    simplest solution  using count  is case-sensitive my string count  m       yields 1 import re   case-sensitive with regex len re findall  m   my string     three ways to get case insensitivity - all yield 2 len re findall    i m   my string   len re findall  m M   my string   len re findall re compile  m  re IGNORECASE   my string     Be aware that the regex version takes on the order of ten times as long to run  which will likely be an issue only if my string is tremendously long  or the code is inside a deep loop

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I know the ask is to count a particular letter  I am writing here generic code without using any method  sentence1   quot  Mary had a little lamb quot  count      for i in sentence1      if i in count          count i lower      count i lower      1     else          count i lower      1 print count   output       5   m   2   a   4   r   1   y   1   h   1   d   1   l   3   i   1   t   2   e   1   b   1   Now if you want any particular letter frequency  you can print like below  print count  m    2

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Python 3   Ther are two ways to achieve this   1  With built-in function count    sentence    Mary had a little lamb  print sentence count  a       2  Without using a function  sentence    Mary had a little lamb      count   0  for i in sentence      if i     a           count   count   1  print count

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An alternative way to get all the character counts without using Counter    count and regex  counts dict      for c in list sentence     if c not in counts dict      counts dict c    0   counts dict c     1  for key  value in counts dict items        print key  value

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a    have a nice day  symbol    abcdefghijklmnopqrstuvwxyz  for key in symbol      print key  a count key

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I don t know about  simplest  but simple comprehension could do   gt  gt  gt  my string    quot Mary had a little lamb quot   gt  gt  gt  sum char     a  for char in my string  4  Taking advantage of built-in sum  generator comprehension and fact that bool is subclass of integer  how may times character is equal to  a

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You can use count       gt  gt  gt   Mary had a little lamb  count  a   4

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count is definitely the most concise and efficient way of counting the occurrence of a character in a string but I tried to come up with a solution using lambda  something like this    sentence    Mary had a little lamb  sum map lambda x   1 if  a  in x else 0  sentence     This will result in    4   Also  there is one more advantage to this is if the sentence is a list of sub-strings containing same characters as above  then also this gives the correct result because of the use of in  Have a look    sentence     M    ar    y    had    a    little    l    am    b   sum map lambda x   1 if  a  in x else 0  sentence     This also results in    4   But Of-course this will work only when checking occurrence of single character such as  a  in this particular case

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Without using count to find you want character in string  method   import re  def count s  ch       pass  def main        s   raw input   Enter strings what you like  for example   welcome            ch   raw input   Enter you want count characters  but best result to find one character          print   len  re findall   ch  s        main

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As other answers said  using the string method count   is probably the simplest  but if you re doing this frequently  check out collections Counter   from collections import Counter my str    Mary had a little lamb  counter   Counter my str  print counter  a

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Regular expressions maybe   import re my string    Mary had a little lamb  len re findall  a   my string

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a    quot I walked today  quot  c   d   e   f   count 0 for i in a      if str i  in c          count  1  print count

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myString count  a      more info here

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No more than this IMHO - you can add the upper or lower methods  def count letter in str string letter       return string count letter

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Python-3 x    aabc  count  a        str count sub   start   end          Return the number of non-overlapping occurrences of substring sub in the range  start  end   Optional arguments start and end are interpreted as in slice notation

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str    count a character occurance   List   list str  print  List  Uniq   set List  print  Uniq   for key in Uniq      print  key  str count key

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This easy and straight forward function might help  def check freq x       freq          for c in set x          freq c    x count c      return freq  check freq  quot abbabcbdbabdbdbabababcbcbab quot     a   7   b   14   c   3   d   3   If a comprehension is desired  def check freq x       return  c  x count c  for c in set x

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spam    have a nice day  var    d    def count spam  var       found   0     for key in spam          if key    var              found    1     return found count spam  var  print  count  s is   s     var  count spam  var

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str count sub   start   end    Return the number of non-overlapping occurrences of substring sub in the range  start  end   Optional arguments start and end are interpreted as in slice notation    gt  gt  gt  sentence    Mary had a little lamb   gt  gt  gt  sentence count  a   4

[python] Count the number occurrences of a character in a string

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