Re: [R] sapply problem

2006-12-15 Thread Joerg van den Hoff 
Sundar Dorai-Raj wrote:
 
 
 Joerg van den Hoff said the following on 12/14/2006 7:30 AM:
 I have encountered the following problem: I need to extract from
 a list of lists equally named compenents who happen to be 'one row'
 data frames. a trivial example would be:

 a - list(list(
 df = data.frame(A = 1, B = 2, C = 3)), list(df = data.frame(A = 4,B = 
 5,C = 6)))

 I want the extracted compenents to fill up a matrix or data frame row 
 by row.
 the obvious thing to do seems:

 b - sapply(a, [[, df)
 b - t(b)

 now `b' looks all right:

 b
 class(b)

 but it turns out that all elements in this matrix are one element lists:

 class(b[1,1])

 which prevents any further standard processing of `b' (like 
 `colMeans', e.g.)

 question 1: is their a straightforward way to enforce that `b' contains
 simple numbers as elements right from the start (instead of something 
 like
 apply(b, 1:2, class-, numeric) afterwards)?

 
 Try this:
 
 a - list(list(df = data.frame(A = 1, B = 2, C = 3)),
   list(df = data.frame(A = 4, B = 5, C = 6)))
 b - do.call(rbind, sapply(a, [, df))
 b
 
 
 question 2: should not sapply do this further 'simplification' anyway 
 in a situation
 like this (matrix elements turn out to be one-element lists)?

 
 I think it does as it much as it knows how. I think you might believe 
 that matrix elements can only contain numeric values. This is not a 
 valid assumption. Take this example:
 
   a - list(1)
   b - list(2)
   (m - matrix(c(a, b), 2, 1))
  [,1]
 [1,] 1
 [2,] 2
   class(m[1, 1])
 [1] list
   class(m[2, 1])
 [1] list
 
 HTH,
 
 --sundar
 
 regards

 joerg


thanks for the help to everybody. the proposal of sundar seems the most concise 
one (if it 
is also efficient I'll see with larger data sets ..).

with regards to my question no. 2: sure I realize that I _can_ have a sensible 
matrix 
consisting of elements that are lists. with regards to `sapply' and the 
intention (as I 
understand it) to simplify as much as is sensible possible (`sapply' unlists 
usually 
everything it can), I think it would be desirable if `sapply' would detect this 
admittedly 
very special case: a matrix of one-element lists whose sole list elements are 
atomic of 
length 1 (which was my case and is exactly your example above).

of course, I don't know whether such a special treatment (probably meaning 
further 
recursive tests in `sapply') would slow down `sapply' significantly in general 
(which 
would be an argument against such a change of `sapply') or maybe it is against 
the actual
purpose of sapply -- I'm not sure.

anyway, thanks again,

joerg

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[R] sapply problem

2006-12-14 Thread Joerg van den Hoff 
I have encountered the following problem: I need to extract from
a list of lists equally named compenents who happen to be 'one row'
data frames. a trivial example would be:

a - list(list(
df = data.frame(A = 1, B = 2, C = 3)), list(df = data.frame(A = 4,B = 5,C = 6)))

I want the extracted compenents to fill up a matrix or data frame row by row.
the obvious thing to do seems:

b - sapply(a, [[, df)
b - t(b)

now `b' looks all right:

b
class(b)

but it turns out that all elements in this matrix are one element lists:

class(b[1,1])

which prevents any further standard processing of `b' (like `colMeans', e.g.)

question 1: is their a straightforward way to enforce that `b' contains
simple numbers as elements right from the start (instead of something like
apply(b, 1:2, class-, numeric) afterwards)?

question 2: should not sapply do this further 'simplification' anyway in a 
situation
like this (matrix elements turn out to be one-element lists)?

regards

joerg

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Re: [R] sapply problem

2006-12-14 Thread jim holtman 
try this:

 b - as.matrix(do.call('rbind', lapply(a,'[[','df')))
 str(b)
 num [1:2, 1:3] 1 4 2 5 3 6
 - attr(*, dimnames)=List of 2
  ..$ : chr [1:2] 1 2
  ..$ : chr [1:3] A B C

 colMeans(b)
  A   B   C
2.5 3.5 4.5
 b
  A B C
1 1 2 3
2 4 5 6




On 12/14/06, Joerg van den Hoff [EMAIL PROTECTED] wrote:

 I have encountered the following problem: I need to extract from
 a list of lists equally named compenents who happen to be 'one row'
 data frames. a trivial example would be:

 a - list(list(
 df = data.frame(A = 1, B = 2, C = 3)), list(df = data.frame(A = 4,B = 5,C
 = 6)))

 I want the extracted compenents to fill up a matrix or data frame row by
 row.
 the obvious thing to do seems:

 b - sapply(a, [[, df)
 b - t(b)

 now `b' looks all right:

 b
 class(b)

 but it turns out that all elements in this matrix are one element lists:

 class(b[1,1])

 which prevents any further standard processing of `b' (like `colMeans',
 e.g.)

 question 1: is their a straightforward way to enforce that `b' contains
 simple numbers as elements right from the start (instead of something like
 apply(b, 1:2, class-, numeric) afterwards)?

 question 2: should not sapply do this further 'simplification' anyway in a
 situation
 like this (matrix elements turn out to be one-element lists)?

 regards

 joerg

 __
 R-help@stat.math.ethz.ch 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.




-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

[[alternative HTML version deleted]]

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Re: [R] sapply problem

2006-12-14 Thread Weiwei Shi 
 c - apply(b, c(1,2), unlist)
 c
 A B C
[1,] 1 2 3
[2,] 4 5 6
 class(c[1,1])
[1] numeric


On 12/14/06, Joerg van den Hoff [EMAIL PROTECTED] wrote:
 I have encountered the following problem: I need to extract from
 a list of lists equally named compenents who happen to be 'one row'
 data frames. a trivial example would be:

 a - list(list(
 df = data.frame(A = 1, B = 2, C = 3)), list(df = data.frame(A = 4,B = 5,C = 
 6)))

 I want the extracted compenents to fill up a matrix or data frame row by row.
 the obvious thing to do seems:

 b - sapply(a, [[, df)
 b - t(b)

 now `b' looks all right:

 b
 class(b)

 but it turns out that all elements in this matrix are one element lists:

 class(b[1,1])

 which prevents any further standard processing of `b' (like `colMeans', e.g.)

 question 1: is their a straightforward way to enforce that `b' contains
 simple numbers as elements right from the start (instead of something like
 apply(b, 1:2, class-, numeric) afterwards)?

 question 2: should not sapply do this further 'simplification' anyway in a 
 situation
 like this (matrix elements turn out to be one-element lists)?

 regards

 joerg

 __
 R-help@stat.math.ethz.ch 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.



-- 
Weiwei Shi, Ph.D
Research Scientist
GeneGO, Inc.

Did you always know?
No, I did not. But I believed...
---Matrix III

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Re: [R] sapply problem

2006-12-14 Thread Sundar Dorai-Raj 


Joerg van den Hoff said the following on 12/14/2006 7:30 AM:
 I have encountered the following problem: I need to extract from
 a list of lists equally named compenents who happen to be 'one row'
 data frames. a trivial example would be:
 
 a - list(list(
 df = data.frame(A = 1, B = 2, C = 3)), list(df = data.frame(A = 4,B = 5,C = 
 6)))
 
 I want the extracted compenents to fill up a matrix or data frame row by row.
 the obvious thing to do seems:
 
 b - sapply(a, [[, df)
 b - t(b)
 
 now `b' looks all right:
 
 b
 class(b)
 
 but it turns out that all elements in this matrix are one element lists:
 
 class(b[1,1])
 
 which prevents any further standard processing of `b' (like `colMeans', e.g.)
 
 question 1: is their a straightforward way to enforce that `b' contains
 simple numbers as elements right from the start (instead of something like
 apply(b, 1:2, class-, numeric) afterwards)?
 

Try this:

a - list(list(df = data.frame(A = 1, B = 2, C = 3)),
   list(df = data.frame(A = 4, B = 5, C = 6)))
b - do.call(rbind, sapply(a, [, df))
b


 question 2: should not sapply do this further 'simplification' anyway in a 
 situation
 like this (matrix elements turn out to be one-element lists)?
 

I think it does as it much as it knows how. I think you might believe 
that matrix elements can only contain numeric values. This is not a 
valid assumption. Take this example:

  a - list(1)
  b - list(2)
  (m - matrix(c(a, b), 2, 1))
  [,1]
[1,] 1
[2,] 2
  class(m[1, 1])
[1] list
  class(m[2, 1])
[1] list

HTH,

--sundar

 regards
 
 joerg
 
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 R-help@stat.math.ethz.ch mailing list
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