grep using a character vector with multiple patterns

Question

I am trying to use grep to test whether a vector of strings are present in an another vector or not  and to output the values that are present  the matching patterns     I have a data frame like this   FirstName Letter    Alex      A1 Alex      A6 Alex      A7 Bob       A1 Chris     A9 Chris     A6   I have a vector of strings patterns to be found in the  Letter  columns  for example  c  A1    A9    A6     I would like to check whether the any of the strings in the pattern vector is present in the  Letter  column  If they are  I would like the output of unique values    The problem is  I don t know how to use grep with multiple patterns  I tried   matches  lt - unique       grep  A1  A9   A6   myfile Letter  value TRUE  fixed TRUE      But it gives me 0 matches which is not true  any suggestions

User · Answer

To add to Brian Diggs answer   another way using grepl will return a data frame containing all your values   toMatch  lt - myfile Letter  matches  lt - myfile grepl paste toMatch  collapse       myfile Letter      matches  Letter Firstname 1     A1      Alex  2     A6      Alex  4     A1       Bob  5     A9     Chris  6     A6     Chris   Maybe a bit cleaner    maybe

User · Answer

Based on Brian Digg s post  here are two helpful functions for filtering lists    Returns all items in a list that are not contained in toMatch  toMatch can be a single item or a list of items exclude  lt - function  theList  toMatch     return setdiff theList include theList toMatch        Returns all items in a list that ARE contained in toMatch  toMatch can be a single item or a list of items include  lt - function  theList  toMatch     matches  lt - unique  grep paste toMatch collapse                                  theList  value TRUE     return matches

User · Answer

This should work  grep pattern    A1 A9 A6   x   myfile Letter   Or even more simply  library data table  myfile Letter  like   A1 A9 A6

User · Answer

Good answers  however don t forget about filter   from dplyr   patterns  lt - c  A1    A9    A6    gt your df   FirstName Letter 1      Alex     A1 2      Alex     A6 3      Alex     A7 4       Bob     A1 5     Chris     A9 6     Chris     A6  result  lt - filter your df  grepl paste patterns  collapse       Letter     gt result   FirstName Letter 1      Alex     A1 2      Alex     A6 3       Bob     A1 4     Chris     A9 5     Chris     A6

User · Answer

I suggest writing a little script and doing multiple searches with Grep   I ve never found a way to search for multiple patterns  and believe me  I ve looked   Like so  your shell file  with an embedded string       bin bash   grep  A6   Alex A1 Alex A6 Alex A7 Bob A1 Chris A9 Chris A6    grep  A7   Alex A1 Alex A6 Alex A7 Bob A1 Chris A9 Chris A6    grep  A8   Alex A1 Alex A6 Alex A7 Bob A1 Chris A9 Chris A6     Then run by typing myshell sh   If you want to be able to pass in the string on the command line  do it like this  with a shell argument--this is bash notation btw       bin bash    stingtomatch      1     grep  A6     stingtomatch     grep  A7     stingtomatch     grep  A8     stingtomatch      And so forth    If there are a lot of patterns to match  you can put it in a for loop

User · Answer

Have you tried the match   or charmatch   functions   Example use   match c  A1    A9    A6    myfile Letter

User · Answer

Using the sapply     patterns  lt - c  A1    A9    A6            df  lt - data frame name c  A   Ale   Al   lex   x   Letters c  A1   A2   A9   A1   A9          name Letters 1    A      A1 2  Ale      A2 3   Al      A9 4  lex      A1 5    x      A9    df unlist sapply patterns  grep  df Letters  USE NAMES   F        name Letters 1    A      A1 4  lex      A1 3   Al      A9 5    x      A9

User · Answer

Not sure whether this answer has already appeared     For the particular pattern in the question  you can just do it with a single grep   call   grep  A 169    myfile Letter

User · Answer

In addition to  Marek s comment about not including fixed  TRUE  you also need to not have the spaces in your regular expression   It should be  A1 A9 A6      You also mention that there are lots of patterns   Assuming that they are in a vector  toMatch  lt - c  A1    A9    A6     Then you can create your regular expression directly using paste and collapse         matches  lt - unique  grep paste toMatch collapse                                myfile Letter  value TRUE

User · Answer

Take away the spaces  So do   matches  lt - unique grep  A1 A9 A6   myfile Letter  value TRUE  fixed TRUE

[r] grep using a character vector with multiple patterns

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