Benjamin Gillespie
2013-Nov-17 14:47 UTC
[R] Extract values from vector and repeat by group
Hi all,
I hope you can help.
I have a data frame 'df':
group=c(rep(1,8),rep(2,10),rep(3,11))
var=rnorm(29)
time=c(seq(1,8),seq(1,10),seq(1,11))
df=data.frame(group,var,time)
I would like to extract the value from 'var' for each 'group' at
'time'=4 and repeat these extracted values in a new vector
('new') n times where n is the number of rows for each group. I did this
by hand as below, but there must be a quicker way:
subset=subset(df,df$time==4)
subset
group var time
4 1 0.2531270 4
12 2 -0.3600128 4
22 3 0.4194730 4
df$new=c(rep(0.2531270,8),rep(-0.3600128,10),rep(0.4194730,11))
Any questions please ask,
Many thanks in advance,
Ben Gillespie, Research Postgraduate
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School of Geography, University of Leeds, Leeds, LS2 9JT
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Tel: +44(0)113 34 33345
Mob: +44(0)770 868 7641
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http://www.geog.leeds.ac.uk/
o-------------------------------------o
@RiversBenG
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On 17-11-2013, at 15:47, Benjamin Gillespie <gybrg at Leeds.ac.uk> wrote:> Hi all, > > I hope you can help. > > I have a data frame 'df': > > group=c(rep(1,8),rep(2,10),rep(3,11)) > var=rnorm(29) > time=c(seq(1,8),seq(1,10),seq(1,11)) > df=data.frame(group,var,time) > > I would like to extract the value from 'var' for each 'group' at 'time'=4 and repeat these extracted values in a new vector ('new') n times where n is the number of rows for each group. I did this by hand as below, but there must be a quicker way: > > subset=subset(df,df$time==4) > subset > group var time > 4 1 0.2531270 4 > 12 2 -0.3600128 4 > 22 3 0.4194730 4 > > df$new=c(rep(0.2531270,8),rep(-0.3600128,10),rep(0.4194730,11)) > > Any questions please ask,A very similar question was recently asked on Stackoverflow: http://stackoverflow.com/questions/19971763/r-programming-normalizing-a-column-of-data-by-another-entry-in-2-other-columns From the answer given there you could try this set.seed(11) # to make it reproducible group=c(rep(1,8),rep(2,10),rep(3,11)) var=rnorm(29) time=c(seq(1,8),seq(1,10),seq(1,11)) df=data.frame(group,var,time) #df #df[df$time==4, c("group", "var")] # merge into original data.frame df <- merge(df, df[df$time == 4, c("group", "var")], by.x = "group", by.y = "group", suffixes = c("", "GroupSK0")) df Berend
Hi probably not most elegant and also not general but rep(df$var[df$time==4],rle(df$group)$lengths) or rep(df$var[df$time==4], sapply(split(df$var,df$group), length)) shall give you desired vector. Regards Petr> -----Original Message----- > From: r-help-bounces at r-project.org [mailto:r-help-bounces at r- > project.org] On Behalf Of Benjamin Gillespie > Sent: Sunday, November 17, 2013 3:47 PM > To: r-help at r-project.org > Subject: [R] Extract values from vector and repeat by group > > Hi all, > > I hope you can help. > > I have a data frame 'df': > > group=c(rep(1,8),rep(2,10),rep(3,11)) > var=rnorm(29) > time=c(seq(1,8),seq(1,10),seq(1,11)) > df=data.frame(group,var,time) > > I would like to extract the value from 'var' for each 'group' at > 'time'=4 and repeat these extracted values in a new vector ('new') n > times where n is the number of rows for each group. I did this by hand > as below, but there must be a quicker way: > > subset=subset(df,df$time==4) > subset > group var time > 4 1 0.2531270 4 > 12 2 -0.3600128 4 > 22 3 0.4194730 4 > > df$new=c(rep(0.2531270,8),rep(-0.3600128,10),rep(0.4194730,11)) > > Any questions please ask, > > Many thanks in advance, > > Ben Gillespie, Research Postgraduate > o-------------------------------------------------------------------o > School of Geography, University of Leeds, Leeds, LS2 9JT o------------- > ------------------------------------------------------o > Tel: +44(0)113 34 33345 > Mob: +44(0)770 868 7641 > o-------------------------------o > http://www.geog.leeds.ac.uk/ > o-------------------------------------o > @RiversBenG > o--------------o > ______________________________________________ > 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.