R help - Mar 2008 - Finding a mean value of a variable holding a dummy variable fixed

I have time-series data on approval ratings of British Prime Ministers.  The
prime ministers dating from MacMillan onward till today are coded as dummy
variables and the approval ratings are entered for each month.  I want to
know the mean value of the approval rating of each Prime Minister in the
dataset and the approval rating during his/her first month and last month as
PM.  What R code should I enter for these data?  In other words, I want hold
the dummy corresponding to each Prime Minister fixed at value one and know
the first rating that PM has, the last rating s/he has, and the mean rating
s/he has.  Thanks.

	[[alternative HTML version deleted]]

The mean problem can be solved with

president=c("Johnson","Johnson","Johnson","Johnson","Johnson","Johnson","Nix
on","Nixon","Nixon","Nixon","Nixon","Nixon")
approval=seq(1:12)
tapply(approval,president,mean)

For the other, I will try to come back. But I am sure somebody will be
faster than I.

Cheers,
Daniel 


-------------------------
cuncta stricte discussurus
-------------------------

-----Urspr?ngliche Nachricht-----
Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Im
Auftrag von Alexander Ovodenko
Gesendet: Sunday, March 30, 2008 9:47 PM
An: r-help at r-project.org
Betreff: [R] Finding a mean value of a variable holding a dummy
variablefixed

I have time-series data on approval ratings of British Prime Ministers.  The
prime ministers dating from MacMillan onward till today are coded as dummy
variables and the approval ratings are entered for each month.  I want to
know the mean value of the approval rating of each Prime Minister in the
dataset and the approval rating during his/her first month and last month as
PM.  What R code should I enter for these data?  In other words, I want hold
the dummy corresponding to each Prime Minister fixed at value one and know
the first rating that PM has, the last rating s/he has, and the mean rating
s/he has.  Thanks.

	[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

I found a solution. It's probably not the easiest one, but it works.  It
assumes that your data frame is ordered from earliest to latest record for
each president, but it can be easily adjusted if you want to make it
dependent on a third column. The final vector "index" gives you the
line
indices for the first record for each president. If you replace "min"
by
"max" you get the last instead of the first record. You can then find
the
values by


##Sample data

president=c("Johnson","Johnson","Johnson","Johnson","Johnson","Johnson","Nix
on","Nixon","Nixon","Nixon","Nixon","Nixon")
approval=c(3,4,5,6,7,8,6,5,4,3,2,1)
tapply(approval,president,mean)

##Find index for first row of each president; assumes ascending order of
observations; change "min" to "max" to find last record

index=NULL
for(i in 1:length(unique(president)))
  index[i]=min(which((president==unique(president)[i])==TRUE))

index

##Generate table with first approvals

first.approval=data.frame(cbind(index,president[index],approval[index]))
names(first.approval)=c("Index","President","Approval")
first.approval

Cheers,
Daniel




-------------------------
cuncta stricte discussurus
-------------------------

-----Urspr?ngliche Nachricht-----
Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Im
Auftrag von Alexander Ovodenko
Gesendet: Sunday, March 30, 2008 9:47 PM
An: r-help at r-project.org
Betreff: [R] Finding a mean value of a variable holding a dummy
variablefixed

I have time-series data on approval ratings of British Prime Ministers.  The
prime ministers dating from MacMillan onward till today are coded as dummy
variables and the approval ratings are entered for each month.  I want to
know the mean value of the approval rating of each Prime Minister in the
dataset and the approval rating during his/her first month and last month as
PM.  What R code should I enter for these data?  In other words, I want hold
the dummy corresponding to each Prime Minister fixed at value one and know
the first rating that PM has, the last rating s/he has, and the mean rating
s/he has.  Thanks.

	[[alternative HTML version deleted]]

______________________________________________
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.