Trying to understand cut

David Winsemius · 2016-04-17T16:39:45Z

> On Apr 16, 2016, at 9:12 PM, John Sorkin wrote: > > Jeff, > Perhaps I was sloppy with my notation: > I want groups >> =0 > =10 > =20 ...... >> =90 > In any event, my question remains, why did the four different versions of cut give me the same results? I hope someone can explain to me the function of > include.lowest and right in the call to cut. As demonstrated in my example below, the parameters do not seem to alter the results of usi

David Winsemius

Sun, Apr 17, 2016 9:39 AM

The pitfalls of using `cut` has pushed me toward a preference for findIntervals

nums<-1:100
table( findInterval( nums ,  seq(0, 100, by=10) ) )

It does mean that I often need to construct names for my groups but at least I know that I will be getting left closed intervals by default, since its `rightmost.closed`-default is FALSE. I often flank my cutting sequence with -Inf on the left and Inf on the right to know that I am seeing any outliers:

table( findInterval( nums ,  c(-Inf, seq(10, 90, by=10), Inf)  )  ) # slightly different

David.


> Thank you,
> John
> 
> 
> P.S. How do I find FAQ 7.31?

On my machine pulling down the Help-menu and choosing "R Help", the R FAQ comes up as a link that will display the full FAQ. I thought the behavior in The Windows R-GUI might be similar, but I lost the ability to use my virtually hosted version of R in my last OS upgrade.

.
> Thank you,
> John
> 
> I 
> 
> 
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing) 
>>>> Jeff Newmiller <jdnewmil at dcn.davis.ca.us> 04/16/16 11:07 PM >>>
> Have you read FAQ 7.31 recently, John? Your whole premise is flawed. You should be thinking of ranges [0,10), [10,20), and so on because numbers ending in 0.9 are never going to be exact. 
> -- 
> Sent from my phone. Please excuse my brevity.
> 
> 
> On April 16, 2016 7:38:50 PM PDT, John Sorkin <jsorkin at grecc.umaryland.edu> wrote:
> I am trying to understand cut so I can divide a list of numbers into 10 group:
>  0-9.0
> 10-10.9
> 20-20.9
> 30-30.9,
> 40-40.9,
> 50-50.9
> 60-60.9
> 70-70.9
> 80-80.9
> 90-90.9
> 
> As I try to do this, I have been playing with the cut function. Surprising the following for applications of cut give me the exact same groups. This surprises me given that I have varied parameters include.lowest and right. Can someone help me understand what include.lowest and right do? I have looked at the help page, but I don't seem to understand what I am being told!
> Thank you,
> John
> 
> values <- c((0:99),c(0.9:99.9))
> sort(values)
> c1<-cut(values,10,include.lowest=FALSE,right=TRUE)
> c2<-cut(values,10,include.lowest=FALSE,right=FALSE)
> c3<-cut(values,10,include.lowest=TRUE,right=TRUE)
> c4<-cut(values,10,include.lowest=TRUE,right=FALSE)
> cbind(min=aggregate(values,list(c1),min),max=aggregate(values,list(c1),max))
> cbind(min=aggregate(values,list(c2),min),max=aggregate(values,list(c2),max))
> cbind(min=aggregate(values,list(c3),min),max=aggregate(values,list(c3),max))
> cbind(min=aggregate(values,list(c4),min),max=aggregate(values,list(c4),max))
> 
> You can run the code below, or inspect the results I got which are reproduced below:
> 
> cbind(min=aggregate(values,list(c1),min),max=aggregate(values,list(c1),max))
> 
>      min.Group.1 min.x    max.Group.1 max.x
> 1  (-0.0999,9.91]     0 (-0.0999,9.91]   9.9
> 2     (9.91,19.9]    10    (9.91,19.9]  19.9
> 3     (19.9,29.9]    20    (19.9,29.9]  29.9
> 4     (29.9,39.9]    30    (29.9,39.9]  39.9
> 5       (39.9,50]    40      (39.9,50]  49.9
> 6         (50,60]    50        (50,60]  59.9
> 7         (60,70]    60        (60,70]  69.9
> 8         (70,80]    70        (70,80]  79.9
> 9         (80,90]    80        (80,90]  89.9
> 10       (90,100]    90       (90,100]  99.9
> cbind(min=aggregate(values,list(c2),min),max=aggregate(values,list(c2),max))
> 
>      min.Group.1 min.x    max.Group.1 max.x
> 1  [-0.0999,9.91)     0 [-0.0999,9.91)   9.9
> 2     [9.91,19.9)    10    [9.91,19.9)  19.9
> 3     [19.9,29.9)    20    [19.9,29.9)  29.9
> 4     [29.9,39.9)    30    [29.9,39.9)  39.9
> 5       [39.9,50)    40      [39.9,50)  49.9
> 6         [50,60)    50        [50,60)  59.9
> 7         [60,70)    60        [60,70)  69.9
> 8         [70,80)    70        [70,80)  79.9
> 9         [80,90)    80        [80,90)  89.9
> 10       [90,100)    90       [90,100)  99.9
> cbind(min=aggregate(values,list(c3),min),max=aggregate(values,list(c3),max))
> 
>      min.Group.1 min.x    max.Group.1 max.x
> 1  [-0.0999,9.91]     0 [-0.0999,9.91]   9.9
> 2     (9.91,19.9]    10    (9.91,19.9]  19.9
> 3     (19.9,29.9]    20    (19.9,29.9]  29.9
> 4     (29.9,39.9]    30    (29.9,39.9]  39.9
> 5       (39.9,50]    40      (39.9,50]  49.9
> 6         (50,60]    50        (50,60]  59.9
> 7         (60,70]    60        (60,70]  69.9
> 8         (70,80]    70        (70,80]  79.9
> 9         (80,90]    80        (80,90]  89.9
> 10       (90,100]    90       (90,100]  99.9
> cbind(min=aggregate(values,list(c4),min),max=aggregate(values,list(c4),max))
> 
>      min.Group.1 min.x    max.Group.1 max.x
> 1 [-0.0999,9.91)     0 [-0.0999,9.91)   9.9
> 2     [9.91,19.9)    10    [9.91,19.9)  19.9
> 3     [19.9,29.9)    20    [19.9,29.9)  29.9
> 4     [29.9,39.9)    30    [29.9,39.9)  39.9
> 5       [39.9,50)    40      [39.9,50)  49.9
> 6         [50,60)    50        [50,60)  59.9
> 7         [60,70)    60        [60,70)  69.9
> 8         [70,80)    70        [70,80)  79.9
> 9         [80,90)    80        [80,90)  89.9
> 10       [90,100]    90       [90,100]  99.9
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing) 
> 
> Confidentiality Statement:
> This email message, including any attachments, isfor t...{{dropped:29}}

Trying to understand cut

Thread (6 messages)