How to fill part of URL in loop

Question

Possible Duplicate:
Read multiple CSV files into separate data frames

How can I fill part of URL with a for loop, I tried one URL it worked, eg:

data <- read.table("http://somelink.php?station=2&start=2012-01-01&etc", header=T,sep="|")

But when I changed the code into a loop, it failed:

station <- c(1:10)
Year <- format(Sys.time(), "%Y")

for (i in station){
data <- read.table("http://somelink.php?station=i&start=Year-01-01&etc", header=T,sep="|")
}

So what help with PHP you need here? Is it tagged PHP only because there is `.php` in your url? — dev-null-dweller, Nov 27 '12 at 23:37
@dev-null-dweller, Sorry about the confusion, I've edited the post — Rosa, Nov 27 '12 at 23:40
@Rosa no problem, I've edited your question to avoid further confusion. Ther is no such thing as `PHP URL`, it is standard format of URL used not only by PHP. — dev-null-dweller, Nov 27 '12 at 23:45

score 3 · Accepted Answer · edited Nov 28 '12 at 00:28

3

The problem is that your iterator i is inside the quotation marks and hence not being evaluated as intended. use paste0(.)

Also, you may want your variable data to be list-like. And perhaps not called data.

myData <- list(length = length(station))
for (i in station){
  urli <- paste0("http://somelink.php?station=", i, "&start=Year-01-01&etc")
  myData[[i]] <- read.table(urli, header=T,sep="|")
}

Edit (mnel)

or more idiomatically

urls <-paste0("http://somelink.php?station=",station, "&start=", Year, "01-01&etc")
myData <- lapply(urls, read.table, header = TRUE, sep = '|')

edited Nov 28 '12 at 00:28

mnel

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answered Nov 28 '12 at 00:23

Ricardo Saporta

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THANK YOU！The station gets running, but I didn't realize that couple of the stations have no data would result in an error, is there a way that can fix the error "no lines available in input"?? – Rosa Nov 28 '12 at 19:11
@rosa can you `dput(urls)` and post it, perhaps in another question? – Ricardo Saporta Nov 28 '12 at 19:31
@mnel,@Ricardo Saporta,I'm not sure if I understand the dput(urls) part, but I rewrited and posted another question, thanks – Rosa Nov 28 '12 at 19:54
@Rosa if you `dput()` an R object, you'll get a string that someone else can paste into their R console to create that object. So if you paste the result of `dput(urls)` into your Stack Overflow question, it makes it a lot easier for people to help you. – Gregor Thomas Dec 03 '12 at 22:32

Erik Shilts · Answer 2 · 2012-12-03T22:25:46.900

1

I'm partial to the sprintf function because it's easy to see what the final string will look like:

station_data <- list()
for (i in station) {
  station_data[[i]] <- read.table(sprintf("http://somelink.php?station=%s&start=Year-01-01&etc", i), 
    header=TRUE, sep="|")
}

edited Dec 03 '12 at 22:25

answered Nov 28 '12 at 00:58

Erik Shilts

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How to fill part of URL in loop

2 Answers2

Edit (mnel)