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Paul Johnston

2009-Feb-11 19:18 UTC

[R] What is going on?

Ok, so I'm new to R, but this is driving me crazy.  In this example, I
am trying to process each element in a list.

<code>
s = "1,2"
l = strsplit(s, ",", fixed=TRUE)
print("BEGIN")
n = length(l)
i = 1
while (i <= n) {
  x = l[[i]]
  print(paste("x:", class(x), x))
  print("BEFORE PRINT")
  print(x)
  print("AFTER PRINT")
  i = i + 1
}
</code>

<actual output>
     [exec] [1] "BEGIN"
     [exec] [1] "x: character 1" "x: character 2"
     [exec] [1] "BEFORE PRINT"
     [exec] [1] "1" "2"
     [exec] [1] "AFTER PRINT"
     [exec] [1] "END"
     [exec] [1] TRUE
</actual output>

<expected output>
     [exec] [1] "BEGIN"
     [exec] [1] "x: character 1"
     [exec] [1] "BEFORE PRINT"
     [exec] [1] "1"
     [exec] [1] "AFTER PRINT"
     [exec] [1] "x: character 2"
     [exec] [1] "BEFORE PRINT"
     [exec] [1] "2"
     [exec] [1] "AFTER PRINT"
     [exec] [1] "END"
     [exec] [1] TRUE
</expected output>

What *basic* concept am I missing here?  The same thing happens with
for (x in l) and lapply(l, function(x) print(x)). Please help.

Peter Alspach

2009-Feb-11 19:42 UTC

head link

[R] What is going on?

Kia ora Paul

length(l) is 1 - that is, it is a list of with one element.  That list
element is a character vector of length 2.

HTH ....

Peter Alspach 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Paul Johnston
> Sent: Thursday, 12 February 2009 8:18 a.m.
> To: r-help at r-project.org
> Subject: [R] What is going on?
> 
> Ok, so I'm new to R, but this is driving me crazy.  In this 
> example, I am trying to process each element in a list.
> 
> <code>
> s = "1,2"
> l = strsplit(s, ",", fixed=TRUE)
> print("BEGIN")
> n = length(l)
> i = 1
> while (i <= n) {
>   x = l[[i]]
>   print(paste("x:", class(x), x))
>   print("BEFORE PRINT")
>   print(x)
>   print("AFTER PRINT")
>   i = i + 1
> }
> </code>
> 
> <actual output>
>      [exec] [1] "BEGIN"
>      [exec] [1] "x: character 1" "x: character 2"
>      [exec] [1] "BEFORE PRINT"
>      [exec] [1] "1" "2"
>      [exec] [1] "AFTER PRINT"
>      [exec] [1] "END"
>      [exec] [1] TRUE
> </actual output>
> 
> <expected output>
>      [exec] [1] "BEGIN"
>      [exec] [1] "x: character 1"
>      [exec] [1] "BEFORE PRINT"
>      [exec] [1] "1"
>      [exec] [1] "AFTER PRINT"
>      [exec] [1] "x: character 2"
>      [exec] [1] "BEFORE PRINT"
>      [exec] [1] "2"
>      [exec] [1] "AFTER PRINT"
>      [exec] [1] "END"
>      [exec] [1] TRUE
> </expected output>
> 
> What *basic* concept am I missing here?  The same thing 
> happens with for (x in l) and lapply(l, function(x) 
> print(x)). Please help.
> 
> ______________________________________________
> 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.
> 
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Ben Bolker

2009-Feb-11 19:43 UTC

head link

[R] What is going on?

The problem is that strsplit is designed to work on a *vector* of
characters (your example is a length-1 vector of characters), each
of which might end up being split into a character vector of different
lengths, so it returns its results as a *list* the same length as
the original character vector: in this case a list of length 1.
> str(l)List of 1
 $ : chr [1:2] "1" "2"

length(l) is 1; length(l[[1]]) is 2.

  Ben Bolker


Paul Johnston-6 wrote:> 
> Ok, so I'm new to R, but this is driving me crazy.  In this example, I
> am trying to process each element in a list.
> 
> <code>
> s = "1,2"
> l = strsplit(s, ",", fixed=TRUE)
> print("BEGIN")
> n = length(l)
> i = 1
> while (i <= n) {
>   x = l[[i]]
>   print(paste("x:", class(x), x))
>   print("BEFORE PRINT")
>   print(x)
>   print("AFTER PRINT")
>   i = i + 1
> }
> </code>
> 
> <actual output>
>      [exec] [1] "BEGIN"
>      [exec] [1] "x: character 1" "x: character 2"
>      [exec] [1] "BEFORE PRINT"
>      [exec] [1] "1" "2"
>      [exec] [1] "AFTER PRINT"
>      [exec] [1] "END"
>      [exec] [1] TRUE
> </actual output>
> 
> <expected output>
>      [exec] [1] "BEGIN"
>      [exec] [1] "x: character 1"
>      [exec] [1] "BEFORE PRINT"
>      [exec] [1] "1"
>      [exec] [1] "AFTER PRINT"
>      [exec] [1] "x: character 2"
>      [exec] [1] "BEFORE PRINT"
>      [exec] [1] "2"
>      [exec] [1] "AFTER PRINT"
>      [exec] [1] "END"
>      [exec] [1] TRUE
> </expected output>
> 
> What *basic* concept am I missing here?  The same thing happens with
> for (x in l) and lapply(l, function(x) print(x)). Please help.
> 
> ______________________________________________
> 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.
> 
> 
-- 
View this message in context:
http://www.nabble.com/What-is-going-on--tp21962284p21962681.html
Sent from the R help mailing list archive at Nabble.com.

Sarah Goslee

2009-Feb-11 19:45 UTC

head link

[R] What is going on?

Lists. You're missing the "list" concept. I'm sure others can
explain it
better, but here's the basic idea.

Take a look at l after you do the split:> l[[1]]
[1] "1" "2"> length(l)[1] 1

strsplit() returns a list of length 1, with two elements, the two
split "bits" of your initial string. The help for strsplit() even
says:

   A list of length 'length(x)' the 'i'-th element of which
contains
     the vector of splits of 'x[i]'.

You can get the individual components that you expected with
l[[1]][1]
and
l[[1]][2]

This is confusing in the single case, but allows strsplit to work on multiple
strings:
> s <- c("1,2", "3,4")
> l = strsplit(s, ",", fixed=TRUE)
> l[[1]]
[1] "1" "2"

[[2]]
[1] "3" "4"
> l[[1]][1]
[1] "1"> l[[2]][1]
[1] "3"> length(l)[1] 2

On Wed, Feb 11, 2009 at 2:18 PM, Paul Johnston <pcj127 at gmail.com>
wrote:> Ok, so I'm new to R, but this is driving me crazy.  In this example, I
> am trying to process each element in a list.
>
> <code>
> s = "1,2"
> l = strsplit(s, ",", fixed=TRUE)
> print("BEGIN")
> n = length(l)
> i = 1
> while (i <= n) {
>  x = l[[i]]
>  print(paste("x:", class(x), x))
>  print("BEFORE PRINT")
>  print(x)
>  print("AFTER PRINT")
>  i = i + 1
> }
> </code>
>
> <actual output>
>     [exec] [1] "BEGIN"
>     [exec] [1] "x: character 1" "x: character 2"
>     [exec] [1] "BEFORE PRINT"
>     [exec] [1] "1" "2"
>     [exec] [1] "AFTER PRINT"
>     [exec] [1] "END"
>     [exec] [1] TRUE
> </actual output>
>
> <expected output>
>     [exec] [1] "BEGIN"
>     [exec] [1] "x: character 1"
>     [exec] [1] "BEFORE PRINT"
>     [exec] [1] "1"
>     [exec] [1] "AFTER PRINT"
>     [exec] [1] "x: character 2"
>     [exec] [1] "BEFORE PRINT"
>     [exec] [1] "2"
>     [exec] [1] "AFTER PRINT"
>     [exec] [1] "END"
>     [exec] [1] TRUE
> </expected output>
>
> What *basic* concept am I missing here?  The same thing happens with
> for (x in l) and lapply(l, function(x) print(x)). Please help.
>
-- 
Sarah Goslee
http://www.functionaldiversity.org

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