R help - Jul 2011 - merge function

Hello,

I'm clearly confused about the merge function. In the following

r <- merge(x,y,all.x=T,all.y=F)

my y vector has only unique values (no duplicates). So I don't understand
how this can ever generate an r which is of greater length than x. 

I thought the default behavior was only matching rows are included, but
that using all.x=T included rows with unmatched x's as well. If all the
y's
are unique, though, I don't understand how length(r) > length(x) is
possible. 

Some clarification would be great.

Thanks,
Mitch


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I was mistaken. There were duplicates in my y vector. Please ignore my
previous message. Sorry. 


-----Original Message-----
From: Downey, Patrick
Sent: Thu 6/30/2011 11:08 PM
To: r-help@r-project.org
Subject: merge function
 
Hello,

I'm clearly confused about the merge function. In the following

r <- merge(x,y,all.x=T,all.y=F)

my y vector has only unique values (no duplicates). So I don't understand
how this can ever generate an r which is of greater length than x. 

I thought the default behavior was only matching rows are included, but
that using all.x=T included rows with unmatched x's as well. If all the
y's
are unique, though, I don't understand how length(r) > length(x) is
possible. 

Some clarification would be great.

Thanks,
Mitch



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You haven't provided a reproducible example.

I do notice you are using T and F which are variables that can be redefined
(which is why TRUE and FALSE are preferred.
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"Downey, Patrick" <PDowney@urban.org> wrote:

Hello,

I'm clearly confused about the merge function. In the following

r <- merge(x,y,all.x=T,all.y=F)

my y vector has only unique values (no duplicates). So I don't understand
how this can ever generate an r which is of greater length than x. 

I thought the default behavior was only matching rows are included, but
that using all.x=T included rows with unmatched x's as well. If all the
y's
are unique, though, I don't understand how length(r) > length(x) is
possible. 

Some clarification would be great.

Thanks,
Mitch


	[[alternative HTML version deleted]]

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