Test if characters are in a string

Question

I m trying to determine if a string is a subset of another string   For example   chars  lt -  test  value  lt -  es    I want to return TRUE if  value  appears as part of the string  chars    In the following scenario  I would want to return false   chars  lt -  test  value  lt -  et

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You can use grep  grep  es    Test    1  1 grep  et    Test   integer 0

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Use the  grepl function grepl  needle  haystack  fixed   TRUE   like so  grepl value  chars  fixed   TRUE    TRUE  Use  grepl to find out more

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Just in case you would also like check if a string  or a set of strings  contain s  multiple sub-strings  you can also use the     between two substrings    gt substring  as at   gt string vector c  ass   ear   eye   heat     gt grepl substring string vector    You will get   1   TRUE FALSE FALSE  TRUE   since the 1st word has substring  as   and the last word contains substring  at

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Similar problem here  Given a string and a list of keywords  detect which  if any  of the keywords are contained in the string   Recommendations from this thread suggest stringr s str detect and grepl  Here are the benchmarks from the microbenchmark package   Using  map keywords   c  once    twice    few   t    yes but only a few times   mapper1  lt - function  x      r   str detect x  map keywords     mapper2  lt - function  x      r   sapply map keywords  function  k  grepl k  x  fixed   T       and then  microbenchmark mapper1 t   mapper2 t   times   5000    we find  Unit  microseconds        expr    min     lq     mean  median      uq      max neval  mapper1 t  26 401 27 988 31 32951 28 8430 29 5225 2091 476  5000  mapper2 t  19 289 20 767 24 94484 23 7725 24 6220 1011 837  5000     As you can see  over 5 000 iterations of the keyword search using str detect and grepl over a practical string and vector of keywords  grepl performs quite a bit better than str detect   The outcome is the boolean vector r which identifies which  if any  of the keywords are contained in the string   Therefore  I recommend using grepl to determine if any keywords are in a string

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You want grepl    gt  chars  lt -  test   gt  value  lt -  es   gt  grepl value  chars   1  TRUE  gt  chars  lt -  test   gt  value  lt -  et   gt  grepl value  chars   1  FALSE

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Use this function from stringi package    gt  stri detect fixed  test  c  et   es     1  FALSE  TRUE   Some benchmarks   library stringi  set seed 123L  value  lt - stri rand strings 10000  ceiling runif 10000  1  100      10000 random ASCII strings head value   chars  lt -  es  library microbenchmark  microbenchmark     grepl chars  value      grepl chars  value  fixed TRUE      grepl chars  value  perl TRUE      stri detect fixed value  chars      stri detect regex value  chars       Unit  milliseconds                                  expr       min        lq    median        uq       max neval                   grepl chars  value  13 682876 13 943184 14 057991 14 295423 15 443530   100     grepl chars  value  fixed   TRUE   5 071617  5 110779  5 281498  5 523421 45 243791   100      grepl chars  value  perl   TRUE   1 835558  1 873280  1 956974  2 259203  3 506741   100       stri detect fixed value  chars   1 191403  1 233287  1 309720  1 510677  2 821284   100       stri detect regex value  chars   6 043537  6 154198  6 273506  6 447714  7 884380   100

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Also  can be done using  stringr  library    gt  library stringr   gt  chars  lt -  test   gt  value  lt -  es   gt  str detect chars  value   1  TRUE      For multiple value case   gt  value  lt - c  es    l    est    a    test    gt  str detect chars  value   1   TRUE FALSE  TRUE FALSE  TRUE

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Answer  Sigh  it took me 45 minutes to find the answer to this simple question  The answer is  grepl needle  haystack  fixed TRUE     Correct  gt  grepl  1 2    1 2   fixed TRUE   1  TRUE  gt  grepl  1 2    123 456   fixed TRUE   1  FALSE    Incorrect  gt  grepl  1 2    1 2    1  FALSE  gt  grepl  1 2    123 456    1  TRUE     Interpretation  grep is named after the linux executable  which is itself an acronym of  Global Regular Expression Print   it would read lines of input and then print them if they matched the arguments you gave   Global  meant the match could occur anywhere on the input line  I ll explain  Regular Expression  below  but the idea is it s a smarter way to match the string  R calls this  character   eg class  abc     and  Print  because it s a command line program  emitting output means it prints to its output string   Now  the grep program is basically a filter  from lines of input  to lines of output  And it seems that R s grep function similarly will take an array of inputs  For reasons that are utterly unknown to me  I only started playing with R about an hour ago   it returns a vector of the indexes that match  rather than a list of matches   But  back to your original question  what we really want is to know whether we found the needle in the haystack  a true false value  They apparently decided to name this function grepl  as in  grep  but with a  Logical  return value  they call true and false logical values  eg class TRUE     So  now we know where the name came from and what it s supposed to do  Lets get back to Regular Expressions  The arguments  even though they are strings  they are used to build regular expressions  henceforth  regex   A regex is a way to match a string  if this definition irritates you  let it go   For example  the regex a matches the character  a   the regex a  matches the character  a  0 or more times  and the regex a  would match the character  a  1 or more times  Hence in the example above  the needle we are searching for 1 2  when treated as a regex  means  one or more 1 followed by a 2     but ours is followed by a plus     So  if you used the grepl without setting fixed  your needles would accidentally be haystacks  and that would accidentally work quite often  we can see it even works for the OP s example  But that s a latent bug  We need to tell it the input is a string  not a regex  which is apparently what fixed is for  Why fixed  No clue  bookmark this answer b c you re probably going to have to look it up 5 more times before you get it memorized   A few final thoughts  The better your code is  the less history you have to know to make sense of it  Every argument can have at least two interesting values  otherwise it wouldn t need to be an argument   the docs list 9 arguments here  which means there s at least 2 9 512 ways to invoke it  that s a lot of work to write  test  and remember    decouple such functions  split them up  remove dependencies on each other  string things are different than regex things are different than vector things   Some of the options are also mutually exclusive  don t give users incorrect ways to use the code  ie the problematic invocation should be structurally nonsensical  such as passing an option that doesn t exist   not logically nonsensical  where you have to emit a warning to explain it   Put metaphorically  replacing the front door in the side of the 10th floor with a wall is better than hanging a sign that warns against its use  but either is better than neither  In an interface  the function defines what the arguments should look like  not the caller  because the caller depends on the function  inferring everything that everyone might ever want to call it with makes the function depend on the callers  too  and this type of cyclical dependency will quickly clog a system up and never provide the benefits you expect   Be very wary of equivocating types  it s a design flaw that things like TRUE and 0 and  abc  are all vectors

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Use grep or grepl but be aware of whether or not you want to use regular expressions   By default  grep and related take a regular expression to match  not a literal substring  If you re not expecting that  and you try to match on an invalid regex  it doesn t work    gt  grep       abc    Error in grep       abc         invalid regular expression      reason  Missing        To do a true substring test  use fixed   TRUE    gt  grep       abc    fixed   TRUE   1  1   If you do want regex  great  but that s not what the OP appears to be asking

[r] Test if characters are in a string

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