â€œRe-writingâ€ the function `MemberQ`

up vote
3
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I am trying to program the function MemberQ using less then possible functions pre defined by Mathematica.
Until this now my code is:

meuMemberQ[f_,n_?NumericQ] /; (Length[Select[f, # == n &]] != 0):=True
meuMemberQ[f_,n_Symbol] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_,n_String] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_, n_] := False

There is a way to writing the same function but without using Select and Length?

Ps: It is just for exercise.

asked Sep 4 at 22:52

Mateus

37216

meuMemberQ2[f_, n_] := Intersection[f, n] === n or meuMemberQ3[f_,n_]:= SubsetQ[f, n]?
â€“Â kglr
Sep 4 at 23:02

So... the ideia is not use others functions. In this case, not using Intersection
â€“Â Mateus
Sep 4 at 23:04

Hint: loop through the list elements and test each with MatchQ. You could use AnyTrue for convenience, or simply Table for a very basic implementation.
â€“Â Szabolcs
Sep 5 at 8:12

add a commentÂ |Â

up vote
3
down vote

favorite

I am trying to program the function MemberQ using less then possible functions pre defined by Mathematica.
Until this now my code is:

meuMemberQ[f_,n_?NumericQ] /; (Length[Select[f, # == n &]] != 0):=True
meuMemberQ[f_,n_Symbol] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_,n_String] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_, n_] := False

There is a way to writing the same function but without using Select and Length?

Ps: It is just for exercise.

asked Sep 4 at 22:52

Mateus

37216

meuMemberQ2[f_, n_] := Intersection[f, n] === n or meuMemberQ3[f_,n_]:= SubsetQ[f, n]?
â€“Â kglr
Sep 4 at 23:02

So... the ideia is not use others functions. In this case, not using Intersection
â€“Â Mateus
Sep 4 at 23:04

Hint: loop through the list elements and test each with MatchQ. You could use AnyTrue for convenience, or simply Table for a very basic implementation.
â€“Â Szabolcs
Sep 5 at 8:12

add a commentÂ |Â

up vote
3
down vote

favorite

I am trying to program the function MemberQ using less then possible functions pre defined by Mathematica.
Until this now my code is:

meuMemberQ[f_,n_?NumericQ] /; (Length[Select[f, # == n &]] != 0):=True
meuMemberQ[f_,n_Symbol] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_,n_String] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_, n_] := False

There is a way to writing the same function but without using Select and Length?

Ps: It is just for exercise.

asked Sep 4 at 22:52

Mateus

37216

I am trying to program the function MemberQ using less then possible functions pre defined by Mathematica.
Until this now my code is:

meuMemberQ[f_,n_?NumericQ] /; (Length[Select[f, # == n &]] != 0):=True
meuMemberQ[f_,n_Symbol] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_,n_String] /; (Length[Select[f, # == n &]] != 0) := True
meuMemberQ[f_, n_] := False

There is a way to writing the same function but without using Select and Length?

Ps: It is just for exercise.

asked Sep 4 at 22:52

Mateus

37216

asked Sep 4 at 22:52

Mateus

37216

asked Sep 4 at 22:52

Mateus

37216

asked Sep 4 at 22:52

Mateus

37216

meuMemberQ2[f_, n_] := Intersection[f, n] === n or meuMemberQ3[f_,n_]:= SubsetQ[f, n]?
â€“Â kglr
Sep 4 at 23:02

So... the ideia is not use others functions. In this case, not using Intersection
â€“Â Mateus
Sep 4 at 23:04

Hint: loop through the list elements and test each with MatchQ. You could use AnyTrue for convenience, or simply Table for a very basic implementation.
â€“Â Szabolcs
Sep 5 at 8:12

add a commentÂ |Â

meuMemberQ2[f_, n_] := Intersection[f, n] === n or meuMemberQ3[f_,n_]:= SubsetQ[f, n]?
â€“Â kglr
Sep 4 at 23:02

So... the ideia is not use others functions. In this case, not using Intersection
â€“Â Mateus
Sep 4 at 23:04

Hint: loop through the list elements and test each with MatchQ. You could use AnyTrue for convenience, or simply Table for a very basic implementation.
â€“Â Szabolcs
Sep 5 at 8:12

meuMemberQ2[f_, n_] := Intersection[f, n] === n or meuMemberQ3[f_,n_]:= SubsetQ[f, n]?
â€“Â kglr
Sep 4 at 23:02

So... the ideia is not use others functions. In this case, not using Intersection
â€“Â Mateus
Sep 4 at 23:04

Hint: loop through the list elements and test each with MatchQ. You could use AnyTrue for convenience, or simply Table for a very basic implementation.
â€“Â Szabolcs
Sep 5 at 8:12

add a commentÂ |Â

2 Answers
2

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up vote
4
down vote

accepted

A recursive implementation:

meuMemberQ[n_, y___, n_] := True;
meuMemberQ[x_, y___, n_] := meuMemberQ[y, n];
meuMemberQ[, n_] := False;

This just cuts through the list step by step looking for an exact match of n_, and if it gets to an empty list it returns False.

It will run into the iteration limit eventually, but if you need to use it with such long lists, there are things that can be done (such as using MemberQ).

answered Sep 4 at 23:10

eyorble

4,2501624

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up vote
4
down vote

A few alternatives:

ClearAll[meuMemberQ2, meuMemberQ3, meuMemberQ4]

meuMemberQ2[f_, n_] := Switch[n, Alternatives @@ f, True, _, False]
meuMemberQ3[f_, n_] := n /. Alternatives@@f ->True, _:> False

meuMemberQ4[OrderlessPatternSequence[n_,___], n_] := True
meuMemberQ4[_,_]:=False

edited Sep 4 at 23:30

answered Sep 4 at 23:23

kglr

159k8183382

add a commentÂ |Â

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

up vote
4
down vote

accepted

A recursive implementation:

meuMemberQ[n_, y___, n_] := True;
meuMemberQ[x_, y___, n_] := meuMemberQ[y, n];
meuMemberQ[, n_] := False;

This just cuts through the list step by step looking for an exact match of n_, and if it gets to an empty list it returns False.

It will run into the iteration limit eventually, but if you need to use it with such long lists, there are things that can be done (such as using MemberQ).

answered Sep 4 at 23:10

eyorble

4,2501624

add a commentÂ |Â

up vote
4
down vote

accepted

A recursive implementation:

meuMemberQ[n_, y___, n_] := True;
meuMemberQ[x_, y___, n_] := meuMemberQ[y, n];
meuMemberQ[, n_] := False;

This just cuts through the list step by step looking for an exact match of n_, and if it gets to an empty list it returns False.

It will run into the iteration limit eventually, but if you need to use it with such long lists, there are things that can be done (such as using MemberQ).

answered Sep 4 at 23:10

eyorble

4,2501624

add a commentÂ |Â

up vote
4
down vote

accepted

A recursive implementation:

meuMemberQ[n_, y___, n_] := True;
meuMemberQ[x_, y___, n_] := meuMemberQ[y, n];
meuMemberQ[, n_] := False;

This just cuts through the list step by step looking for an exact match of n_, and if it gets to an empty list it returns False.

It will run into the iteration limit eventually, but if you need to use it with such long lists, there are things that can be done (such as using MemberQ).

answered Sep 4 at 23:10

eyorble

4,2501624

A recursive implementation:

meuMemberQ[n_, y___, n_] := True;
meuMemberQ[x_, y___, n_] := meuMemberQ[y, n];
meuMemberQ[, n_] := False;

This just cuts through the list step by step looking for an exact match of n_, and if it gets to an empty list it returns False.

It will run into the iteration limit eventually, but if you need to use it with such long lists, there are things that can be done (such as using MemberQ).

answered Sep 4 at 23:10

eyorble

4,2501624

answered Sep 4 at 23:10

eyorble

4,2501624

answered Sep 4 at 23:10

eyorble

4,2501624

answered Sep 4 at 23:10

eyorble

4,2501624

add a commentÂ |Â

up vote
4
down vote

A few alternatives:

ClearAll[meuMemberQ2, meuMemberQ3, meuMemberQ4]

meuMemberQ2[f_, n_] := Switch[n, Alternatives @@ f, True, _, False]
meuMemberQ3[f_, n_] := n /. Alternatives@@f ->True, _:> False

meuMemberQ4[OrderlessPatternSequence[n_,___], n_] := True
meuMemberQ4[_,_]:=False

edited Sep 4 at 23:30

answered Sep 4 at 23:23

kglr

159k8183382

add a commentÂ |Â

up vote
4
down vote

A few alternatives:

ClearAll[meuMemberQ2, meuMemberQ3, meuMemberQ4]

meuMemberQ2[f_, n_] := Switch[n, Alternatives @@ f, True, _, False]
meuMemberQ3[f_, n_] := n /. Alternatives@@f ->True, _:> False

meuMemberQ4[OrderlessPatternSequence[n_,___], n_] := True
meuMemberQ4[_,_]:=False

edited Sep 4 at 23:30

answered Sep 4 at 23:23

kglr

159k8183382

add a commentÂ |Â

up vote
4
down vote

A few alternatives:

ClearAll[meuMemberQ2, meuMemberQ3, meuMemberQ4]

meuMemberQ2[f_, n_] := Switch[n, Alternatives @@ f, True, _, False]
meuMemberQ3[f_, n_] := n /. Alternatives@@f ->True, _:> False

meuMemberQ4[OrderlessPatternSequence[n_,___], n_] := True
meuMemberQ4[_,_]:=False

edited Sep 4 at 23:30

answered Sep 4 at 23:23

kglr

159k8183382

A few alternatives:

ClearAll[meuMemberQ2, meuMemberQ3, meuMemberQ4]

meuMemberQ2[f_, n_] := Switch[n, Alternatives @@ f, True, _, False]
meuMemberQ3[f_, n_] := n /. Alternatives@@f ->True, _:> False

meuMemberQ4[OrderlessPatternSequence[n_,___], n_] := True
meuMemberQ4[_,_]:=False

edited Sep 4 at 23:30

answered Sep 4 at 23:23

kglr

159k8183382

edited Sep 4 at 23:30

answered Sep 4 at 23:23

kglr

159k8183382

answered Sep 4 at 23:23

kglr

159k8183382

answered Sep 4 at 23:23

kglr

159k8183382

add a commentÂ |Â

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