Hello,
I have two character vectors: list.a and list.b. Every element of list.a
appears somewhere in list.b. Not all elements of list.b are in list.a, and
some elements of list.b appear multiple times in list.a. I want to create a
new vector (index) of the same length as list.a where the nth element of
index is the location in list.b of the nth element of list.a.
This code will work, but I have heard over and over again that using loops
is inefficient in R and that there are (almost always) better ways to do
things.
for(i in 1:length(list.a)){
index[i] <- seq(1,length(list.b))[list.b==list.a[i]]
}
Thank you,
Mitch
match(list.a,list.b) - Phil Spector Statistical Computing Facility Department of Statistics UC Berkeley spector at stat.berkeley.edu On Fri, 8 Apr 2011, Downey, Patrick wrote:> Hello, > > I have two character vectors: list.a and list.b. Every element of list.a > appears somewhere in list.b. Not all elements of list.b are in list.a, and > some elements of list.b appear multiple times in list.a. I want to create a > new vector (index) of the same length as list.a where the nth element of > index is the location in list.b of the nth element of list.a. > > This code will work, but I have heard over and over again that using loops > is inefficient in R and that there are (almost always) better ways to do > things. > > for(i in 1:length(list.a)){ > index[i] <- seq(1,length(list.b))[list.b==list.a[i]] > } > > Thank you, > Mitch > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >
Perfect. Thank you. -Mitch -----Original Message----- From: Phil Spector [mailto:spector at stat.berkeley.edu] Sent: Friday, April 08, 2011 8:03 PM To: Downey, Patrick Cc: r-help at r-project.org Subject: Re: [R] Finding elements in a character vector match(list.a,list.b) - Phil Spector Statistical Computing Facility Department of Statistics UC Berkeley spector at stat.berkeley.edu On Fri, 8 Apr 2011, Downey, Patrick wrote:> Hello, > > I have two character vectors: list.a and list.b. Every element of > list.a appears somewhere in list.b. Not all elements of list.b are in > list.a, and some elements of list.b appear multiple times in list.a. I > want to create a new vector (index) of the same length as list.a where > the nth element of index is the location in list.b of the nth element oflist.a.> > This code will work, but I have heard over and over again that using > loops is inefficient in R and that there are (almost always) better > ways to do things. > > for(i in 1:length(list.a)){ > index[i] <- seq(1,length(list.b))[list.b==list.a[i]] > } > > Thank you, > Mitch > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >