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exists vs. member vs. memq

Yaosan

When checking if certain item can be found in a list, we can use either exists or member:

exists( i '("a" "b" "c") i == "b" )

member( "b" '("a" "b" "c") )

I'm wondering if one of them is faster than the other.Since SKILL Lint always suggest to use memq instead of member,using exists will avoid those suggestion from showing up.

Now that we have a list of string, memq can't be used. Does it make sense to convert our list of string to list of symbol first then use memq to optimize this process? (assume the list can be short or very long i.e. more than 500 elements)

For example:

myList = '("a" "b" "c")
memq( 'b foreach( mapcar i myList concat(i) ) )

As mentioned in the beginning, all we care is if an item can be found in the list i.e. whether the return is nil or non-nil. Thanks for any feedback.

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  • dmay

    If performance is most important, then use a table.

    myTbl = makeTable("myTbl" nil)
    myTbl["a"]=t
    myTbl["b"]=t
    myTbl["c"]=t
    or
    foreach(item myList
        myTbl[item]=t
    )
    then check for existence in the table:
    if(myTbl[x] then ...

    The table will be MUCH faster than using member/memq/exists for lists.

    Derek

Reply
  • dmay

    If performance is most important, then use a table.

    myTbl = makeTable("myTbl" nil)
    myTbl["a"]=t
    myTbl["b"]=t
    myTbl["c"]=t
    or
    foreach(item myList
        myTbl[item]=t
    )
    then check for existence in the table:
    if(myTbl[x] then ...

    The table will be MUCH faster than using member/memq/exists for lists.

    Derek

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