Message-ID: <2222330D-1F9A-414F-A237-E2600CEB4093@gmail.com>
Date: 2013-06-12T11:54:19Z
From: Peter Dalgaard
Subject: change factor to mtrix
In-Reply-To: <CAKO0Dpjo9GcB3ay78bpnsqpYA1MVvT-DTTU5Sf9enO18zgwasw@mail.gmail.com>
On Jun 12, 2013, at 09:47 , Gallon Li wrote:
> i wish to change a column of factor variable to multiple columns of
> zero-ones
>
> for example, my factor could be
>
> ff=c('a','a','b','b','c','c')
>
> then I want to have two columns (for three levels) that are
>
> 0 0
> 0 0
> 1 0
> 1 0
> 0 1
> 0 1
>
> how can i do this fast?
Maybe not fast, but quick:
> fff <- factor(ff)
> model.matrix(~fff)[,-1]
fffb fffc
1 0 0
2 0 0
3 1 0
4 1 0
5 0 1
6 0 1
Possibly faster, skipping some "red tape":
> CC <- contrasts(fff)
> CC
b c
a 0 0
b 1 0
c 0 1
> CC[fff,]
b c
a 0 0
a 0 0
b 1 0
b 1 0
c 0 1
c 0 1
>
> [[alternative HTML version deleted]]
>
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--
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk Priv: PDalgd at gmail.com