Dewez Thomas
2004-Sep-01 15:41 UTC
[R] coercing a string naming to a variable name and return value
Hi all,
I haven't been able to find how to assess a variable who's name is
constructed with paste. The problem is following: In a data frame, there are
12 columns whose title vary only by a digit, all other part being equal. I
would like to compute a operation on a subset these variables and parse them
in turn.
the data frame "basin.param" contains columns called ratio1, ratio2,
ratio3...
in each of these ratios I want to retain only values above 0. This could be
put like this
crit<- which(basin.param$ratio1 > 0)
basin.param$ratio1[crit] + basin.param$val[crit]
OK, so what if I want to increment from ratio1 to ratio3 automatically and
return the value of the variable represented by the string? (does this make
sense?)
# Create the variable name
for (i in 1:3){
string.variable <- paste("basin.param$ratio", index,
sep="")
# What is the instruction to interpret the string.variable value ???
}
Cheers
Thomas
***
Le contenu de cet e-mail et de ses pi??ces jointes est destin...{{dropped}}
Roger D. Peng
2004-Sep-01 15:50 UTC
[R] coercing a string naming to a variable name and return value
You can use "[[", I think, as in basin.param[[string.variable]] or, eqivalently for a data frame basin.param[, string.variable] -roger Dewez Thomas wrote:> Hi all, > > I haven't been able to find how to assess a variable who's name is > constructed with paste. The problem is following: In a data frame, there are > 12 columns whose title vary only by a digit, all other part being equal. I > would like to compute a operation on a subset these variables and parse them > in turn. > > the data frame "basin.param" contains columns called ratio1, ratio2, > ratio3... > in each of these ratios I want to retain only values above 0. This could be > put like this > > crit<- which(basin.param$ratio1 > 0) > basin.param$ratio1[crit] + basin.param$val[crit] > > OK, so what if I want to increment from ratio1 to ratio3 automatically and > return the value of the variable represented by the string? (does this make > sense?) > # Create the variable name > for (i in 1:3){ > string.variable <- paste("basin.param$ratio", index, sep="") > # What is the instruction to interpret the string.variable value ??? > } > > Cheers > > Thomas > *** > Le contenu de cet e-mail et de ses pi??ces jointes est destin...{{dropped}} > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html >
Sundar Dorai-Raj
2004-Sep-01 15:55 UTC
[R] coercing a string naming to a variable name and return value
Dewez Thomas wrote:> Hi all, > > I haven't been able to find how to assess a variable who's name is > constructed with paste. The problem is following: In a data frame, there are > 12 columns whose title vary only by a digit, all other part being equal. I > would like to compute a operation on a subset these variables and parse them > in turn. > > the data frame "basin.param" contains columns called ratio1, ratio2, > ratio3... > in each of these ratios I want to retain only values above 0. This could be > put like this > > crit<- which(basin.param$ratio1 > 0) > basin.param$ratio1[crit] + basin.param$val[crit] > > OK, so what if I want to increment from ratio1 to ratio3 automatically and > return the value of the variable represented by the string? (does this make > sense?) > # Create the variable name > for (i in 1:3){ > string.variable <- paste("basin.param$ratio", index, sep="") > # What is the instruction to interpret the string.variable value ??? > } >You're better off using the data.frame names with the "[" operator and not the data.frame name itself with the "$" operator. How about: val <- list() for(i in 1:3) { ratCol <- paste("ratio", i, sep = "") ratio.i <- basin.param[, ratCol] crit <- ratio.i > 0 val[[ratCol]] <- ratio.i[crit] + basin.param$val[crit] } --sundar
Adaikalavan Ramasamy
2004-Sep-01 16:03 UTC
[R] coercing a string naming to a variable name and return value
I am not sure if I understand your problem but I think you might be
close to the solution. Perhaps if you changed 'index' in your code to
'i', you might get the answer. Try this :
set.seed(1066)
m <- matrix(rnorm(9), nc=3)
colnames(m) <- paste("ratio", 1:3, sep="")
m
ratio1 ratio2 ratio3
[1,] -0.5917632 0.2399853 2.810498
[2,] 0.2926060 0.9197199 -0.977170
[3,] -0.9212630 -0.7864827 1.746278
for(i in 1:3){
name <- paste("ratio", i, sep="")
values <- m[ , name]
cat("Column named", name, "has values", values,
"\n") }
}
Column named ratio1 has values -0.5917632 0.2926060 -0.921263
Column named ratio2 has values 0.2399853 0.9197199 -0.7864827
Column named ratio3 has values 2.810498 -0.97717 1.746278
for(i in c(2,3,1)){
cat("Column named", name <- paste("ratio", i,
sep=""),
"has values", m[ , name], "\n")
}
Column named ratio2 has values 0.2399853 0.9197199 -0.7864827
Column named ratio3 has values 2.810498 -0.97717 1.746278
Column named ratio1 has values -0.5917632 0.2926060 -0.921263
On Wed, 2004-09-01 at 16:41, Dewez Thomas wrote:> Hi all,
>
> I haven't been able to find how to assess a variable who's name is
> constructed with paste. The problem is following: In a data frame, there
are
> 12 columns whose title vary only by a digit, all other part being equal. I
> would like to compute a operation on a subset these variables and parse
them
> in turn.
>
> the data frame "basin.param" contains columns called ratio1,
ratio2,
> ratio3...
> in each of these ratios I want to retain only values above 0. This could be
> put like this
>
> crit<- which(basin.param$ratio1 > 0)
> basin.param$ratio1[crit] + basin.param$val[crit]
>
> OK, so what if I want to increment from ratio1 to ratio3 automatically and
> return the value of the variable represented by the string? (does this make
> sense?)
> # Create the variable name
> for (i in 1:3){
> string.variable <- paste("basin.param$ratio", index,
sep="")
> # What is the instruction to interpret the string.variable value ???
> }
>
> Cheers
>
> Thomas
> ***
> Le contenu de cet e-mail et de ses pi??ces jointes est destin...{{dropped}}
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>