# Replace elements that match pattern

I am using pattern matching to identify elements in a list to be replaced. How can I supply a list of patterns to match and replace all elements in the list that match the pattern? The problem I have now is that each replacement generates a new list. But what I want is a single list with all pattern matched elements replaced. Thus far I have tried,

x={k1p->0.214161,km1->35.8125,k2p->0.3880,km2->39.57}/.
PatternSequence[#->_]->#>0.0&/@{k1p,k2p}
(*{{k1p->0.,km1->35.8125,k2p->0.388,km2->39.57},{k1p->0.214161,km1->35.8125,k2p->0.388,km2->0.}}*)


And I've tried to use replace repeated (//.) Which does give a single list, however nothing is replaced.

x={k1p->0.214161,km1->35.8125,k2p->0.3880,km2->39.57}//.PatternSequence[#->_]->#->0.0&/@{{k1p,km2}}
(*{{k1p->0.214161,km1->35.8125,k2p->0.388,km2->39.57}}*)


## 1 Answer

expr = {k1p -> 0.214161, km1 -> 35.8125, k2p -> 0.3880, km2 -> 39.57};
expr /. PatternSequence[p : k1p | k2p -> _] -> (p -> 0.0)
(* or expr /. Rule[p:k1p|k2p,_] :> Rule[p,0.0] *)
(* {k1p -> 0., km1 -> 35.8125, k2p -> 0., km2 -> 39.57} *)


More generally,

lst = {km1, k2p, km2};
exprs /. Rule[p : Alternatives @@ lst, _] :> Rule[p, 0.0]
(* {k1p -> 0.214161, km1 -> 0., k2p -> 0., km2 -> 0.} *)

• Great! But suppose that I change the replacement list from {k1p,k2p} to {km1,k2p,km2}. How could I alter the above to automatically act on the new replacement list of arbitrary length? Commented Mar 7, 2015 at 20:30
• @tarhawk, please see the update.
– kglr
Commented Mar 7, 2015 at 20:33