Select rows from a data frame based on values in a vector

Question

I have data similar to this   dt  lt - structure list fct   structure c 1L  2L  3L  4L  3L  4L  1L  2L  3L  1L  2L  3L  2L  3L  4L    Label   c  a    b    c    d    class    factor    X   c 2L  4L  3L  2L  5L  4L  7L  2L  9L  1L  4L  2L  5L  4L  2L     Names   c  fct    X    class    data frame   row names   c NA  -15L     I want to select rows from this data frame based on the values in the fct variable  For example  if I wish to select rows containing either  a  or  c  I can do this   dt dt fct     a    dt fct     c       which yields   1    a 2 3    c 3 5    c 5 7    a 7 9    c 9 10   a 1 12   c 2 14   c 4   as expected  But my actual data is more complex and I actually want to select rows based on the values in a vector such as  vc  lt - c  a    c     So I tried  dt dt fct    vc      but of course that doesn t work  I know I could code something to loop through the vector and pull out the rows needed and append them to a new dataframe  but I was hoping there was a more elegant way   So how can I filter subset my data based on the contents of the vector vc

User · Accepted Answer

Have a look at    in     dt dt fct  in  vc      fct X 1    a 2 3    c 3 5    c 5 7    a 7 9    c 9 10   a 1 12   c 2 14   c 4   You could also use  is element   dt is element dt fct  vc

User · Answer

Another option would be to use a keyed data table   library data table  setDT dt  key    fct   J vc      or  setDT dt  key    fct     vc     which results in      fct X 1    a 2 2    a 7 3    a 1 4    c 3 5    c 5 6    c 9 7    c 2 8    c 4   What this does    setDT dt  key    fct   transforms the data frame to a data table  which is an enhanced form of a data frame  with the fct column set as key  Next you can just subset with the vc vector with  J vc      NOTE  when the key is a factor character variable  you can also use setDT dt  key    fct   vc  but that won t work when vc is a numeric vector  When vc is a numeric vector and is not wrapped in J   or      vc will work as a rowindex   A more detailed explanation of the concept of keys and subsetting can be found in the vignette Keys and fast binary search based subset   An alternative as suggested by  Frank in the comments   setDT dt  J vc   on   fct       When vc contains values that are not present in dt  you ll need to add nomatch   0   setDT dt  key    fct   J vc   nomatch   0    or   setDT dt  J vc   on   fct   nomatch   0

User · Answer

Similar to above  using filter from dplyr   filter df  fct  in  vc

[r] Select rows from a data frame based on values in a vector

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