#I have a dataframe called "tests" that contain "character
expressions". These
characters are rules that use data from within another dataframe. Is there
any way within R I can access the rules in the dataframe called tests, and
then "evaluate" these "rules"?
#An example may better explain what I am trying to accomplish:
tests <- data.frame(matrix(data=c("info$country ==
'Greenland'", "info$age> 50"), nrow=2, ncol=1))
names(tests) <- "rule"
info <- data.frame(matrix(data=NA, nrow=5, ncol=3))
names(info) <- c("first", "country", "age")
info$name <- c("Mary", "Paul", "Robert",
"John", "Ivan")
info$country <- c("GReenland", "Iceland",
"Ireland", "Greenland",
"Greenland")
info$age <- c(30, 55, 66, 79, 80)
#e.g. for
"info$country == 'Greenland'"
#I want:
info$country == 'Greenland'
[1] FALSE FALSE FALSE TRUE TRUE
#e.g.
info$country == 'Greenland'
info$age > 50
#I tried this, but it does not "work":
eval(tests$rule[1])
[[alternative HTML version deleted]]
Hello,
I've changed the way you create data.frame 'tests', like it was the
conditions were factors, which are coded as integers. We need them of
class character to be parsed. Note that the same could be done with the
data.frame 'info' but it's not absolutely needed.
tests <- data.frame(rule=c("info$country == 'Greenland'",
"info$age > 50"),
stringsAsFactors=FALSE)
str(tests)
tests
#------------------ This does the trick
fun <- function(x){
f <- function(){} # an empty function, no body
force(x) # evaluate the argument
body(f) <- parse(text=x) # parse it and assign the function
f # return the function
}
# See if it works
expr1 <- fun(tests$rule[1]) # This creates a function
expr1()
Hope this helps,
Rui Barradas
Em 03-07-2012 17:24, New RUser escreveu:> #I have a dataframe called "tests" that contain "character
expressions". These
> characters are rules that use data from within another dataframe. Is there
> any way within R I can access the rules in the dataframe called tests, and
> then "evaluate" these "rules"?
>
>
>
> #An example may better explain what I am trying to accomplish:
>
>
>
> tests <- data.frame(matrix(data=c("info$country ==
'Greenland'", "info$age
>> 50"), nrow=2, ncol=1))
>
> names(tests) <- "rule"
>
>
>
> info <- data.frame(matrix(data=NA, nrow=5, ncol=3))
>
> names(info) <- c("first", "country",
"age")
>
> info$name <- c("Mary", "Paul", "Robert",
"John", "Ivan")
>
> info$country <- c("GReenland", "Iceland",
"Ireland", "Greenland",
> "Greenland")
>
> info$age <- c(30, 55, 66, 79, 80)
>
>
>
> #e.g. for
>
> "info$country == 'Greenland'"
>
>
>
> #I want:
>
> info$country == 'Greenland'
>
> [1] FALSE FALSE FALSE TRUE TRUE
>
> #e.g.
> info$country == 'Greenland'
>
> info$age > 50
>
>
>
> #I tried this, but it does not "work":
>
> eval(tests$rule[1])
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
Hello,
Your "eval(tests$rule[1])" needs a slight modification to get the
results.
Try this:
tests<-read.table(text="
?rule
?info$country=='Greenland'
?info$age>50
?",sep="",header=TRUE,stringsAsFactors=FALSE)
info<-data.frame(first=rep(NA,5),country=c("GReenland","Iceland","Ireland","Greenland","Greenland")
,age=c(30,55,66,79,80),name=c("Mary","Paul","Robert","John","Ivan"))
#1st condition
eval(parse(text=tests$rule[1]))
[1] FALSE FALSE FALSE? TRUE? TRUE
#2nd condition
eval(parse(text=tests$rule[2]))
[1] FALSE? TRUE? TRUE? TRUE? TRUE
# tests[1,1] condition: subset info
info[eval(parse(text=tests$rule[1])),]
? first?? country age name
4??? NA Greenland? 79 John
5??? NA Greenland? 80 Ivan
#tests[2,1] condition: subset info
info[eval(parse(text=tests$rule[2])),]
? first?? country age?? name
2??? NA?? Iceland? 55?? Paul
3??? NA?? Ireland? 66 Robert
4??? NA Greenland? 79?? John
5??? NA Greenland? 80?? Ivan
A.K.
----- Original Message -----
From: New RUser <newruser2012 at gmail.com>
To: r-help at r-project.org
Cc:
Sent: Tuesday, July 3, 2012 12:24 PM
Subject: [R] "evaluating expressions" contained in a dataframe
#I have a dataframe called "tests" that contain "character
expressions".? These
characters are rules that use data from within another dataframe.? Is there
any way within R I can access the rules in the dataframe called tests, and
then "evaluate" these "rules"?
#An example may better explain what I am trying to accomplish:
tests <- data.frame(matrix(data=c("info$country ==
'Greenland'", "info$age> 50"), nrow=2, ncol=1))
names(tests) <- "rule"
info <- data.frame(matrix(data=NA, nrow=5, ncol=3))
names(info) <- c("first", "country", "age")
info$name <- c("Mary", "Paul", "Robert",
"John", "Ivan")
info$country <- c("GReenland", "Iceland",
"Ireland", "Greenland",
"Greenland")
info$age <- c(30, 55, 66, 79, 80)
#e.g. for
"info$country == 'Greenland'"
#I want:
info$country == 'Greenland'
[1] FALSE FALSE FALSE? TRUE? TRUE
#e.g.
info$country == 'Greenland'
info$age > 50
#I tried this, but it does not "work":
eval(tests$rule[1])
??? [[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.