R help - May 2008 - Extracting slots from ROCR prediction objects

Hi,

I have an object from the prediction function from the ROCR package and I would
like to extract one of the slots from the object, for example the cutoffs slot.
However the usual techniques ($, [["name"]]) of subsetting don't
work. How can I assess the lists in the slots?

Here is an example of what I am working with:

library(ROCR)
data(ROCR.simple)
pred <- prediction(ROCR.simple$predictions,ROCR.simple$labels)
> str(pred)
Formal class 'prediction' [package "ROCR"] with 11 slots
  ..@ predictions:List of 1
  .. ..$ : num [1:200] 0.613 0.364 0.432 0.140 0.385 ...
  ..@ labels     :List of 1
  .. ..$ : Ord.factor w/ 2 levels "0"<"1": 2 2 1 1 1 2 2
2 2 1 ...
  ..@ cutoffs    :List of 1
  .. ..$ : num [1:201]   Inf 0.991 0.985 0.985 0.983 ...
  ..@ fp         :List of 1
  .. ..$ : num [1:201] 0 0 0 0 1 1 2 3 3 3 ...
  ..@ tp         :List of 1
  .. ..$ : num [1:201] 0 1 2 3 3 4 4 4 5 6 ...
  ..@ tn         :List of 1
  .. ..$ : num [1:201] 107 107 107 107 106 106 105 104 104 104 ...
  ..@ fn         :List of 1
  .. ..$ : num [1:201] 93 92 91 90 90 89 89 89 88 87 ...
  ..@ n.pos      :List of 1
  .. ..$ : int 93
  ..@ n.neg      :List of 1
  .. ..$ : int 107
  ..@ n.pos.pred :List of 1
  .. ..$ : num [1:201] 0 1 2 3 4 5 6 7 8 9 ...
  ..@ n.neg.pred :List of 1
  .. ..$ : num [1:201] 200 199 198 197 196 195 194 193 192 191
...
> 
Thanks in advance,
Stacey

       
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Hi Stacey,
Try this:

library(ROCR)
data(ROCR.simple)
pred <- prediction(ROCR.simple$predictions,ROCR.simple$labels)
perf <- performance(pred,"sens","spec")
cuts <- unlist(slot(perf,"alpha.values"))
cuts

HTH,

Jorge


On Thu, May 22, 2008 at 2:08 PM, Stacey Burrows <stacey.burrows@yahoo.ca>
wrote:
> Hi,
>
> I have an object from the prediction function from the ROCR package and I
> would like to extract one of the slots from the object, for example the
> cutoffs slot. However the usual techniques ($, [["name"]]) of
subsetting
> don't work. How can I assess the lists in the slots?
>
> Here is an example of what I am working with:
>
> library(ROCR)
> data(ROCR.simple)
> pred <- prediction(ROCR.simple$predictions,ROCR.simple$labels)
>
> > str(pred)
> Formal class 'prediction' [package "ROCR"] with 11 slots
>  ..@ predictions:List of 1
>  .. ..$ : num [1:200] 0.613 0.364 0.432 0.140 0.385 ...
>  ..@ labels     :List of 1
>  .. ..$ : Ord.factor w/ 2 levels "0"<"1": 2 2 1 1 1
2 2 2 2 1 ...
>  ..@ cutoffs    :List of 1
>  .. ..$ : num [1:201]   Inf 0.991 0.985 0.985 0.983 ...
>  ..@ fp         :List of 1
>  .. ..$ : num [1:201] 0 0 0 0 1 1 2 3 3 3 ...
>  ..@ tp         :List of 1
>  .. ..$ : num [1:201] 0 1 2 3 3 4 4 4 5 6 ...
>  ..@ tn         :List of 1
>  .. ..$ : num [1:201] 107 107 107 107 106 106 105 104 104 104 ...
>  ..@ fn         :List of 1
>  .. ..$ : num [1:201] 93 92 91 90 90 89 89 89 88 87 ...
>  ..@ n.pos      :List of 1
>  .. ..$ : int 93
>  ..@ n.neg      :List of 1
>  .. ..$ : int 107
>  ..@ n.pos.pred :List of 1
>  .. ..$ : num [1:201] 0 1 2 3 4 5 6 7 8 9 ...
>  ..@ n.neg.pred :List of 1
>  .. ..$ : num [1:201] 200 199 198 197 196 195 194 193 192 191 ...
> >
>
> Thanks in advance,
> Stacey
>
>
> ---------------------------------
>
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