count of entries in data frame in R

Question

I m looking to get a count for the following data frame    gt  Santa    Believe Age Gender Presents Behaviour 1    FALSE   9   male       25   naughty 2     TRUE   5   male       20      nice 3     TRUE   4 female       30      nice 4     TRUE   4   male       34   naughty   of the number of children who believe  What command would I use to get this    The actual data frame is much bigger  I ve just given you the first four rows      Thanks

User · Answer

sum Santa Believe

User · Answer

You could use table   R gt  x  lt - read table textConnection      Believe Age Gender Presents Behaviour 1    FALSE   9   male       25   naughty 2     TRUE   5   male       20      nice 3     TRUE   4 female       30      nice 4     TRUE   4   male       34   naughty     header TRUE   R gt  table x Believe   FALSE  TRUE      1     3

User · Answer

DPLYR makes this really easy    x lt -santa  gt      count Believe    If you wanted to count by a group  for instance  how many males v females believe  just add a group by   x lt -santa  gt      group by Gender   gt      count Believe

User · Answer

I think of this as a two-step process     subset the original data frame according to the filter supplied  Believe  FALSE   then get the row count of this subset   For the first step  the subset function is a good way to do this  just an alternative to ordinary index or bracket notation    For the second step  i would use dim or nrow  One advantage of using subset  you don t have to parse the result it returns to get the result you need--just call nrow on it directly   so in your case   v   nrow subset Santa  Believe  FALSE          subset  returns a data frame   or wrapped in an anonymous function    gt  gt  fnx   function fac  lev  nrow subset Santa  fac  lev      gt  gt  fnx Believe  TRUE        3   Aside from nrow  dim will also do the job  This function returns the dimensions of a data frame  rows  cols  so you just need to supply the appropriate index to access the number of rows    v   dim subset Santa  Believe  FALSE   1     An answer to the OP posted before this one shows the use of a contingency table  I don t like that approach for the general problem as recited in the OP  Here s the reason  Granted  the general problem of how many rows in this data frame have value x in column C  can be answered using a contingency table as well as using a  filtering  scheme  as in my answer here   If you want row counts for all values for a given factor variable  column  then a contingency table  via calling table and passing in the column s  of interest  is the most sensible solution  however  the OP asks for the count of a particular value in a factor variable  not counts across all values  Aside from the performance hit  might be big  might be trivial  just depends on the size of the data frame and the processing pipeline context in which this function resides   And of course once the result from the call to table is returned  you still have to parse from that result just the count that you want    So that s why  to me  this is a filtering rather than a cross-tab problem

User · Answer

You can do summary santa Believe  and you will get the count for TRUE and FALSE

User · Answer

A one-line solution with data table could be  library data table  setDT x    N by Believe     Believe N 1    FALSE 1 2     TRUE 3

User · Answer

using sqldf fits here   library sqldf  sqldf  SELECT Believe  Count 1  as N FROM Santa        GROUP BY Believe

[r] count of entries in data frame in R

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