R help - Jun 2012 - Printing a variable in a loop

Dear R Users:

I'm a STATA user converting to R, and I'd like to be to do the
following.
#Assign var_1 and var_2 a value
10->var1
20->var2

#Now I'd like to print the values of var_1 and var_2 by looping through
var_1 and var_2 in such a manner:

while(y<3){
  print(var_y)
y+1->y
}

In STATA, the "y" appended to " var_" is called the local
variable and the
code would look like this:

while y<3 (
display var`y'
y=y+1
)

Stata would understand that `y' is first 1 and then 2, and print out the
values assigned to var_1 and var_2. Is there a way to do this in R? How
would R users fram this questions even? What terminology would you use?

Thanks!


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Hi Kat,

On Thu, Jun 28, 2012 at 8:22 AM, kat_the_great <knv4 at hotmail.com>
wrote:
> Dear R Users:
>
> I'm a STATA user converting to R, and I'd like to be to do the
following.
> #Assign var_1 and var_2 a value
> 10->var1
> 20->var2
>
> #Now I'd like to print the values of var_1 and var_2 by looping through
> var_1 and var_2 in such a manner:
>
> while(y<3){
> ?print(var_y)
> y+1->y
> }
The nearest you can get is

while (y < 3) {
  print(.GlobalEnv[[paste("var", y, sep="")]])
  y <- y + 1
}

.GlobalEnv (a list, or strictly speaking an environment) contains all
variables at the top-level of the REPL

But this is not how we do it in R.

1. if you want to "display" the variable, just type it
> var1
2. In Stata, you are working with one (tabular) data set at any time.
In R, you can work with multiple data sets (R construct: dataframes)
at the same time. For example using the builtin anscombe data set

Stata:

use anscombe
di x1 y1 x2 y2   // display all
di x1 y1 x2 y2 if _n <= 10


R:

# data(anscombe)           # optional
anscombe[, c("x1", "y1", "x2", "y2")]  
# index by column
anscombe[1:10, c("x1", "y1", "x2",
"y2")]  # index by row & column
head(anscombe[, c("x1","y1","x2","y2")],
n=10]   # same as above




Regards,

Jon

Hello,

  Can't you just use vectors? Untested example:

  var[1] <- 10
  var[2] <- 20
  y <- 1
  while(y < 3) {
    print(var[y])
    y <- y+1
  }

     Take care
     Oliver

On Wed, Jun 27, 2012 at 8:22 PM, kat_the_great <knv4 at hotmail.com>
wrote:
> Dear R Users:
>
> I'm a STATA user converting to R, and I'd like to be to do the
following.
> #Assign var_1 and var_2 a value
> 10->var1
> 20->var2
>
> #Now I'd like to print the values of var_1 and var_2 by looping through
> var_1 and var_2 in such a manner:
>
> while(y<3){
> ?print(var_y)
> y+1->y
> }
>
> In STATA, the "y" appended to " var_" is called the
local variable and the
> code would look like this:
>
> while y<3 (
> display var`y'
> y=y+1
> )
>
> Stata would understand that `y' is first 1 and then 2, and print out
the
> values assigned to var_1 and var_2. Is there a way to do this in R? How
> would R users fram this questions even? What terminology would you use?
>
> Thanks!
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Printing-a-variable-in-a-loop-tp4634673.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.


-- 
Oliver Ruebenacker, Bioinformatics and Network Analysis Consultant
President and Founder of Knowomics
(http://www.knowomics.com/wiki/Oliver_Ruebenacker)
Consultant at Predictive Medicine
(http://predmed.com/people/oliverruebenacker.html)
SBPAX: Turning Bio Knowledge into Math Models (http://www.sbpax.org)

Thanks for your reply Jon. 

I need to actually do more than print the name of the variable (I just made
the example simpler). I need to manipulate var_1, var_2 etc. but setting
values of NA to 0. 

 So as you said, "1. if you want to "display" the variable, just
type it 
>var_1
"

But how do I do this in a loop where the  number portion of var is the
counter in the loop?

Thanks!
Kat

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Hi
> 
> Thanks for your reply Jon. 
> 
> I need to actually do more than print the name of the variable (I just 
made
> the example simpler). I need to manipulate var_1, var_2 etc. but setting
> values of NA to 0. 
Why? R has pretty strong system for handling NAs. The only exception AFAIK 
is cumsum
x<-1:10
sum(x)
[1] 55
x[5]<-NA
sum(x)
[1] NA
sum(x, na.rm=T)
[1] 50
cumsum(x)
 [1]  1  3  6 10 NA NA NA NA NA NA
> 
>  So as you said, "1. if you want to "display" the variable,
just type it
> >var_1
> "
> 
> But how do I do this in a loop where the  number portion of var is the
> counter in the loop?
You probably shall get familiar with list concept which is another strong 
feature of R. You can easily subset lists either by *apply functions or in 
for cycle just by indexing.
> 
> Thanks!
> Kat
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Printing-a-
> variable-in-a-loop-tp4634673p4634754.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> 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.