Count number of occurences for each unique value

Question

Let s say I have   v   rep c 1 2  2  2   25    Now  I want to count the number of times each unique value appears  unique v   returns what the unique values are  but not how many they are     gt  unique v   1  1 2   I want something that gives me   length v v  1    1  25 length v v  2    1  75   but as a more general one-liner    Something close  but not quite  like this     lt doesn t work right gt  length v v  unique v

User · Answer

It is a one-line approach by using aggregate     gt  aggregate data frame count   v   list value   v   length     value count 1     1    25 2     2    75

User · Answer

This works for me  Take your vector v  length summary as factor v  maxsum 50000    Comment  set maxsum to be large enough to capture the number of unique values  or with the magrittr package  v   gt   as factor   gt   summary maxsum 50000    gt   length

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length unique df col   is the most simple way I can see

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If you need to have the number of unique values as an additional column in the data frame containing your values  a column which may represent sample size for example   plyr provides a neat way   data frame  lt - data frame v   rep c 1 2  2  2   25    library  plyr   data frame  lt - ddply data frame    v   transform  n   length v

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To get an un-dimensioned integer vector that contains the count of unique values  use c      dummyData   rep c 1  2  2  2   25    Chase s reproducible data c table dummyData     get un-dimensioned integer vector  1  2  25 75  str c table dummyData       confirm structure  Named int  1 2  25 75  - attr     names    chr  1 2   1   2    This may be useful if you need to feed the counts of unique values into another function  and is shorter and more idiomatic than the t as data frame table dummyData    2  posted in a comment to Chase s answer  Thanks to Ricardo Saporta who pointed this out to me here

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count unique words  lt -function wlist    ucountlist   list   unamelist   c   for  i in wlist    if  is element i  unamelist       ucountlist  i    lt - ucountlist  i    1 else           listlen  lt - length ucountlist      ucountlist  i    lt - 1     unamelist  lt - c unamelist  i          ucountlist    expt counts  lt - count unique words population  for i in names expt counts       cat i  expt counts  i      n

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Perhaps table is what you are after   dummyData   rep c 1 2  2  2   25   table dummyData    dummyData    1  2    25 75     or another presentation of the same data as data frame table dummyData        dummyData Freq    1         1   25    2         2   75

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If you have multiple factors    a multi-dimensional data frame   you can use the dplyr package to count unique values in each combination of factors   library  dplyr   data   gt   group by factor1  factor2    gt   summarize count n      It uses the pipe operator   gt   to chain method calls on the data frame data

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If you want to run unique on a data frame  e g   train data   and also get the counts  which can be used as the weight in classifiers   you can do the following   unique count   function train data  all numeric FALSE                                                                                                                                                                                                         first convert each row in the data frame to a string                                                                                                                                                                                 train data str   apply train data  1  function x  paste x  collapse                                                                                                                                                                      use table to index and count the strings                                                                                                                                                                                             train data str t   table train data str                                                                                                                                                                                                  get the unique data string from the row names                                                                                                                                                                                        train data str uniq   row names train data str t                                                                                                                                                                                       weight   as numeric train data str t                                                                                                                                                                                                     convert the unique data string to data frame   if  all numeric        train data uniq   as data frame t apply cbind train data str uniq   1         function x  as numeric unlist strsplit x  split                                                                                                                   else       train data uniq   as data frame t apply cbind train data str uniq   1         function x  unlist strsplit x  split                                                                                                                    names train data uniq    names train data                                                                                                                                                                                              list data train data uniq  weight weight

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I know there are many other answers  but here is another way to do it using the sort and rle functions  The function rle stands for Run Length Encoding  It can be used for counts of runs of numbers  see the R man docs on rle   but can also be applied here  test data   rep c 1  2  2  2   25  rle sort test data      Run Length Encoding      lengths  int  1 2  25 75      values   num  1 2  1 2  If you capture the result  you can access the lengths and values as follows     rle returns a list with two items  result counts  lt - rle sort test data   result counts lengths     1  25 75 result counts values     1  1 2

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Also making the values categorical and calling summary   would work    gt  v   rep as factor c 1 2  2  2    25   gt  summary v   1  2  25 75

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You can try also a tidyverse  library tidyverse   dummyData   gt        as tibble     gt        count value    A tibble  2 x 2   value     n    lt dbl gt   lt int gt  1     1    25 2     2    75

User · Answer

table   function is a good way to go  as Chase suggested  If you are analyzing a large dataset  an alternative way is to use  N function in datatable package   Make sure you installed the data table package by   install packages  data table     Code     Import the data table package library data table     Generate a data table object  which draws a number 10 7 times     from 1 to 10 with replacement DT lt -data table x sample 1 10 1E7 TRUE      Count Frequency of each factor level DT   N by x

[r] Count number of occurences for each unique value

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