Creating Variables via String Inputs

Question

I am trying to create a loop that generates variables. But I need a way to name the variables using an input method. What is the convention for inputting string names in variable generating

x="Variable" y="weight" z="height"

xy=paste(x,y,sep="") xz=paste(x,y,sep="")

xy_one=1:10 xy_two=11:20

So xy_one should be named VariableWeight_one and xz_two should be names Variableheight_two

IRTFM · Accepted Answer · 2013-12-08 20:08:06Z

1

Agree with Carl not to do it that way but I think his approach could be improved by using "[[" rather than "$". Try:

myVars<-list()
x="Variable"; y="Weight"; z="Height"
myVars[[ paste(x,y,"_one", sep="")]] <- 1:10
myVars[[ paste(x,z,"_one", sep="")]] <- 11:20

If you really still want to construct names I'll compose a suitable addition:

 x="Variable"; y="Weight"; z="Height"
 assign( paste(x,y,"_one", sep=""),  1:10)
 assign( paste(x,z,"_one", sep=""), 11:20)
 ls(patt="Variable")
[1] "VariableHeight_one" "VariableWeight_one"

Compare the effort (and language circumlocutions) it might take to find the first variable you created using your approach with with how simple it would be to extract the first element from myVars:

 eval(parse( text=ls(patt="Variable")[1] ))
# [1] 11 12 13 14 15 16 17 18 19 20

  myVars[[1]]
# [1]  1  2  3  4  5  6  7  8  9 10

(Furthermore, it wasn't even the right one.)

edited Dec 8, 2013 at 20:08

answered Dec 8, 2013 at 20:01

IRTFM

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Carl Witthoft · Accepted Answer · 2013-12-08 19:31:09Z

1

The real answer is: don't do it that way. It's much easier, and more productive, to create a list or dataframe variable, dump your data into elements of same, and then assign names to these elements. In your case,

mydata<- list()
mydata$VariableWeight_one <- xy_one
mydata$Variableheight_two <- xy_two

answered Dec 8, 2013 at 19:31

Carl Witthoft

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3 Comments

jessica Over a year ago

Thank you for the repsonse Carl. But at the end of the day, I am trying to create a way to generate variables throughout a loop. I need the convention used in R to input strings into variables names.

jessica Over a year ago

for (i in c("abe","john","ryan","carl") {i_score=i}

Carl Witthoft Over a year ago

@jessica then you'll have to look into the infamous eval(parse(foo)) construct -- or DWin's assign() method.

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