# [Haskell] How to substract a list?

Bright Sun bright_sun at yahoo.com
Sun Mar 27 19:28:27 EST 2005

```Hi,

Tks, this is not what I wanted.

I want remove pairs list,

[(5,1),(4,1),(3,1),(2,1),(1,1)] remove [(2,1),(1,1)]
[(5,1),(4,1),(3,1)]

so pairs [(2,1),(1,1)] removed.

Tks.

--- Pierre Barbier de Reuille
> One answer is the infix operator (\\) defined in the
> List module (or in
> Data.List ...)
>
> But it's in ont of the "set" operations. For example
> try :
>
> [1..10] \\ [3..6]
> [1,2,7,8,9,10]
>
> But also :
>
> ([1..10]++[1..10]) \\ [3..6]
> [1,2,7,8,9,10,1,2,7,8,9,10]
>
> So _all_ the elements with values in [3..6] where
> removed !!
> If that's what you want ! Perfect ... if not : what
> do you want exactly
> ? List substraction is not uniq.
>
> Pierre
>
> Bright Sun a écrit :
> > In Haskell, ++ can spends second list argument
> onto
> > the end of first list argument.  How to substract
> the
> > second list from the first list?
> >
> > For example,
> > [(5,1),(4,1),(3,1),(2,1),(1,1)]
> > substract
> > [(2,1),(1,1)]
> > I want to get result list:
> > [(5,1),(4,1),(3,1)]
> >
> > Tks.
> >
> >
> >
> > __________________________________
> > Do you Yahoo!?
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> > _______________________________________________
> >
>
> --
> Pierre Barbier de Reuille
>
> INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP
> Botanique et Bio-informatique de l'Architecture des
> Plantes
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>
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>

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