[R] How to add specific column to data.set?

[R. Michael Weylandt]

I'll unpack it bit by bit:

stringsAsFactors = FALSE is a command to tell R how to construct the
data frame: this doesn't apply to you because you already have a data
frame, but I need it to set up my examples. By default, when you give
R data that looks like strings/labels, it wants to convert those to
factors (category data), but this stops that behavior and keeps the
characters. This is considered by many to be a bad default, but it's
so fundamental to the language that it couldn't be changed now without
breaking lots of code. Perhaps something we'll see in an R 3.0 if that
ever happens.

lapply(countries, function(x) x %in% euro) -- function(x) x%in% euro
simply checks for each x which elements are in the european union and
returns logical (True/False) values -- the lapply call goes column by
column (here just the two in my example) because data.frames are
really lists and each column is a list element. This latter point is
somewhat subtle so don't worry too much about it just yet -- I could
have done apply(, 2, ) and it would be just as good.

Reduce -- takes a list of arguments and combines them sequentially
with another function, here `&` (the AND function) -- For instance, a
sum function could be written as Reduce(`+`, inputs) e.g.,
Reduce(`+`, list(1,2,3,4)) = 1 + Reduce(`+`, list(2,3,4)) = 1 + 2 +
Reduce(`+`, list(3,4)) = 3 + 3 + Reduce(`+`, list(4)) = 6 + 4 = 10 --
for this example, it checks all the countries (just two columns) and
ANDs them (per your request)

cbind -- attaches a new column

dput simply converts an object to plain text so it can be emailed
easily -- the console printout doesn't give enough information for us
to reproduce your problem/data, but dput will. It's not specific to
your problem -- just a mailing list / reproducibility hint.

Hope this helps,

Michael



On Wed, Apr 18, 2012 at 2:24 AM, phillip03 <phillipbrigham at hotmail.com> wrote:
> Wow it works :) Thank you SO much!!
> I am very new at R and was thinking if you would explain what these to codes
> do:
>
> countries<-data.frame(country1,country2,stringsAsFactors=FALSE)
>
> # I know this i a vector with both my county lists but what does
> stringsAsFacors= FALSE do ?. What if I wantede a row with 1=TRUE and 0=FALSE
>
> and
>
>
> cbind(countries,EMU=Reduce(`&`, lapply(countries,
> + function(x) x %in% euro)))
>
> # here I columnbind my new defined vector and produce a new one ? What does
> the Reduce and lapply do ?
>
>
> I am also not quite sure of the dput() you wrote michael sorry. I understand
> if you dont have the time to help further :)
>
> Ph
>
> --
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