R help - Jul 2009 - How to use macro variable in a text string

I want to use read.table to input many files, each for a different year.  I
would like to use the macro variable 't' to refer to the exact file that
I
would like to input the data using read.table.  How could I do this?  Thank
you!

for (t in 1970:2005)
{ edge <- read.table(file="edge_t.csv", header=T, 
sep=",")
## I will  have many rows of code following the read.table line 
}

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Hi,

On Jul 22, 2009, at 5:46 PM, kxk wrote:
> I want to use read.table to input many files, each for a different  
> year.  I
> would like to use the macro variable 't' to refer to the exact file
> that I
> would like to input the data using read.table.  How could I do  
> this?  Thank
> you!
>
> for (t in 1970:2005)
> { edge <- read.table(file="edge_t.csv", header=T, 
sep=",")
> ## I will  have many rows of code following the read.table line
> }
Two things:

1. Not extremely important here at all, but for the future: just note  
that but by using "t" you're trampling over the transpose function
t(), so perhaps you can use a more descriptive variable to both make  
code more readable and less ... urm, trample-itve :-)

2. Answer:

for (year in 1970:2005) {
   edge <- read.table(file=sprintf("edge_%d.csv", year), header=T,
sep=",")
   ...
}

You can also use the paste function in place of sprintf

-steve

--
Steve Lianoglou
Graduate Student: Physiology, Biophysics and Systems Biology
Weill Medical College of Cornell University

Contact Info: http://cbio.mskcc.org/~lianos/contact

On Jul 22, 2009, at 5:46 PM, kxk wrote:
>
> I want to use read.table to input many files, each for a different  
> year.  I
> would like to use the macro variable 't' to refer to the exact file
> that I
> would like to input the data using read.table.  How could I do  
> this?  Thank
> you!
>
> for (t in 1970:2005)
> { edge <- read.table(file="edge_t.csv", header=T, 
sep=",")
Pretty sure that will not work. Take a look at the paste function for  
putting together strings and values.

paste("test", 1:3, sep="")

#[1] "test1" "test2" "test3"

And you might consider whether you want "edge" to be wiped out the  
next time through the loop, too. That is what would happen with your  
current construction.

> ## I will  have many rows of code following the read.table line
> }
>
> --
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

Dear kxk,
Here are a couple of options:

# Option 1 -- sapply
mydata <- sapply(1970:2005, function(i){
                      mydata <- read.table(file = paste("edge_", i,
".csv",
sep=""), header=TRUE)
                     # more code goes here
                    }
                  )

Please note that mydata would be a list, so to access the data for 1970,
type mydata[[1]] in the R Console.

# Option 2  -- create a function foo
Another possibility would be to create a function, e.g foo, that reads the
data in and does the procedures you need for each file. It would be
something like:

foo <- function(nameFile){
          mydata <- read.table(file = paste("edge_", nameFile,
".csv",
sep=""), header=T)
         # more code goes here
             }

To do what you want for one file, just type

onefile <- foo(1970)

in the R Console. To do all your files at once, then

myresults <- sapply(1970:2005, foo)

is what you need. Once again, myresults would be a list.

Now, If you insist using a for loop, then

1. Avoid to use "t". It is an R function. See ?t
2. Rewrite your loop as

edge <- NULL
for (i in 1970:2005){
          edge[[i]] <- read.table(file = paste("edge_", i,
".csv", sep=""),
header=TRUE)
         # more code goes here
           }

3. Use the "[[" operator to extract the information you need from
"edge".

Also, you might be interested in the foreach package <
http://cran.r-project.org/web/packages/foreach/>. Take a look at the
Vignette that come with it.

See ?sapply and ?"for" for more details.

HTH,

Jorge



On Wed, Jul 22, 2009 at 5:46 PM, kxk <kkong@u.washington.edu> wrote:
>
> I want to use read.table to input many files, each for a different year.  I
> would like to use the macro variable 't' to refer to the exact file
that I
> would like to input the data using read.table.  How could I do this?  Thank
> you!
>
> for (t in 1970:2005)
> { edge <- read.table(file="edge_t.csv", header=T, 
sep=",")
> ## I will  have many rows of code following the read.table line
> }
>
> --
> View this message in context:
>
http://www.nabble.com/How-to-use-macro-variable-in-a-text-string-tp24615030p24615030.html
> Sent from the R help mailing list archive at Nabble.com.
>
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