how to subset unique factor combinations from a data frame.

Hi,

Sorry that my example is not clear. I will give an example of what each
variable holds. I hope this clearly explains the case.

Names of the dataframe (df) and description

Year :- Year is calendar year, from 1980 to 2010

Country :- is the country name, total no. (levels) of countries is ~ 190 

Commodity :- Crude oil, Sugar, Rubber, Coffee .... No. (levels) of
commodities is 20

Attribute: - Production, Consumption, Stock, Import, Export... Levels ~ 20

Unit :- this is actually not a factor. It describes the unit of Attribute.
Say the unit for Coffee (commodity) - Production (attribute) is 60 kgs.
While the unit for Crude oil - Production is 1000 barrels

Value :-  value

tail(df, n = 10) // example data//

Year	Country		Commodity	Attribute	Unit
Value
1991	United Kingdom	Wheat, Durum	Total Supply	(1000 MT)	70
1991	United Kingdom	Wheat, Durum	TY Exports	(1000 MT)	0
1991	United Kingdom	Wheat, Durum	TY Imp. from U	(1000 MT)	0
1991	United Kingdom	Wheat, Durum	TY Imports	(1000 MT)	60
1991	United Kingdom	Wheat, Durum	Yield		(MT/HA)	5

Wish this is clear. Any suggestion

Regards,

SNVK

-----Original Message-----
From: Petr PIKAL [mailto:petr.pikal at precheza.cz] 
Sent: Tuesday, January 04, 2011 4:06 PM
To: SNV Krishna
Cc: r-help at r-project.org
Subject: Odp: [R] how to subset unique factor combinations from a data
frame.

Hi

r-help-bounces at r-project.org napsal dne 04.01.2011 05:21:25:

Hi All

I have these questions and request members expert view on this. 

a) I have a dataframe (df) with five factors (identity variables) and

value

(measured value). The id variables are Year, Country, Commodity,

Attribute,

Unit. Value is a value for each combination of this.

I would like to get just the unique combination of Commodity, 
Attribute

and

Unit. I just need the unique factor combination into a dataframe or a

table.

I know aggregate and subset but dont how to use them in this context. 

aggregate(Value, list(Comoditiy, Atribute, Unit), function)

b) Is it possible to inclue non- aggregate columns with aggregate

function

say in the above case > aggregate(Value ~ Commodity + Attribute, data 
=

df,

FUN = count). The use of count(Value) is just a round about to return

the

combinations of Commodity & Attribute, and I would like to include

'Unit'

column in the returned data frame?

Hm. Maybe xtabs? But without any example it is only a guess.

c) Is it possible to subset based on unique combination, some thing 
like this.

subset(df, unique(Commodity), select = c(Commodity, Attribute, Unit)). 

I

know this is not correct as it returns an error 'subset needs a 
logical evaluation'. Trying various ways to accomplish the task.

Probably sqldf package has tools for doing it but I do not use it so you
have to try yourself.

df[Comodity==something, c("Commodity", "Attribute", "Unit")]

can be other way.

Anyway your explanation is ambiguous. Let say you have three rows with the
same Commodity. Which row do you want to select?

Regards
Petr

will be grateful for any ideas and help

Regards,

SNVK

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