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$rule[2])),]
first country age name
2 NA Iceland 55 Paul
3 NA Ireland 66 Robert
4 NA Greenland 79 John
5 NA Greenland 80 Ivan
A.K.
----- Original Message -----
From: New RUser <newruser2...@gmail.com>
To: r-help@r-project.org
Cc:
Sent: Tuesday, July 3, 2012 12:24 PM
Subject: [R] "evaluating expressions" contained in a dataframe
#I have a dataframe called "tests" that contain "character expressions". These
characters are rules that use data from within another dataframe. Is there
any way within R I can access the rules in the dataframe called tests, and
then "evaluate" these "rules"?
#An example may better explain what I am trying to accomplish:
tests <- data.frame(matrix(data=c("info$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])
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and provide commented, minimal, self-contained, reproducible code.
