[R] Merge data frames but with a twist.

[Stephen Tucker]

You may want to use the reshape package for this task:

> library(reshape)
> recast(DF3,Show ~ Datetime, id.var=names(DF3),value="Measure")
       Show 08/26/2009 11:30 AM 08/26/2009 9:30 AM
1   Firefly                   3                  1
2 Red Dwarf                   4                  2

If you want to plot time series, you can do something like the following

> mydf <- .Last.value ## save the output from above to mydf
> library(zoo)
> zobj <- zoo(`mode<-`(t(mydf),"numeric"),
>             as.chron(strptime(names(mydf)[-1],"%m/%d/%Y %I:%M %p")))
> plot(zobj)

(zobj is a time series object of the zoo class)



----- Original Message ----
From: Tony Breyal <tony.breyal at googlemail.com>
To: r-help at r-project.org
Sent: Thursday, August 27, 2009 4:04:30 AM
Subject: [R] Merge data frames but with a twist.

Dear all,

Question: How to merge two data frames such that new column are added
in a particular way?

I'm not actually sure how to best articulate my question to be honest,
so i hope showing you what I want to achieve will communicate my
question better.

Lets say I have two data frames:

> DF1 <- data.frame(cbind(Show=c('Firefly', 'Red Dwarf'), Measure=1:2, Datetime=c('08/26/2009 9:30 AM', '08/26/2009 9:30 AM')))

> DF2 <- data.frame(cbind(Show=c('Firefly', 'Red Dwarf'), Measure=3:4, Datetime=c('08/26/2009 11:30 AM', '08/26/2009 11:30 AM')))

And then let us merge these:

> DF3 <- merge(DF1, DF2, all=TRUE)

       Show         Measure            Datetime
1     Firefly         1                      08/26/2009 9:30 AM
2     Firefly         3                      08/26/2009 11:30 AM
3     Red Dwarf   2                      08/26/2009 9:30 AM
4     Red Dwarf   4                      08/26/2009 11:30 AM


What i would like to do is merge the data frames such that i end up
with the following:

Show           08/26/2009 9:30 AM        08/26/2009 11:30 AM
Firefly          1                                    3
Red Dwarf    2                                    4

my reason for doing this is so that i can plot a time series somehow.

I hope the formating stays when i post this message and that what i'm
trying to do is easy to understand. Thank you kindly for any help in
advance.

Tony

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