Applying several patterns to `Split`

Question

Please consider the following:

Split[data, patterns &]
patterns=Not[#=="a"]&&Not[#=="b"]&&...&&Not[#=="blabla"];

How can I define patterns without typing &&Not[#=="char"] for every single pattern?

Answer 1

You can add some syntactic sugar to do that relatively easily. For example, define a head for that:

ClearAll[SplitPattern];
SplitPattern /: Split[expr_, SplitPattern[pt_]] :=
   Split[expr, MatchQ[#, pt] &];

And use this as follows:

lst = {"a", "b", "c", "d", "blabla", "e", "f"}
Split[lst,SplitPattern[Except["a"|"b"|"blabla"]]]

(*  {{a},{b},{c,d,blabla},{e,f}} *)

The performance may not be that great, but I guess the question was more about convenience.

Answer 2

It looks like you really want to use set of different dividers, in that case, you can simply test using a function that checks whether the current element is a member of your set of deviders:

 dividers = {3, 4, 5}
 Split[Range@10, ! MemberQ[dividers, #] &]

To answer your litteral question, your patterns is basically And taken over a range of structurally identical terms that are functions of a list of dividers, so you could use Map and Apply

patterns= Function[t, And @@ (Not[t == #] & /@ {"a", "b", "blabla"})]

Then you can use

lst = {"a", "b", "c", "d", "blabla", "e", "f"}
Split[lst,patterns]

{{"a"}, {"b"}, {"c", "d", "blabla"}, {"e", "f"}}

In a similar fasion, if you just wanted to combine a seriues of different test you could use And@@{test1[#],test2[#],test3[#]}&.

I hope this helps.

Answer 3

Another option is to create a temporary function which evaluates to False for your target strings and True otherwise.

splitAt[data_, x_] := Module[{f},
  (f[#, _] = False) & /@ x;
  f[__] = True;
  Split[data, f]]

lst = {"a", "b", "c", "d", "blabla", "e", "f"} ;
splitAt[lst, {"a", "b", "blabla"}]

(* {{"a"}, {"b"}, {"c", "d", "blabla"}, {"e", "f"}} *)