[R] coercing a string naming to a variable name and return value

Dewez Thomas t.dewez at brgm.fr
Wed Sep 1 17:41:24 CEST 2004

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,
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
# 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 ???


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