RE: [R] Bug on the stem function or in my brain ?

From: Ignacio Colonna <iacolonn_at_uiuc.edu>
Date: Tue 22 Mar 2005 - 03:41:45 EST


Josť,

        Notice that the values to the left of the | in your stem plot are all even. Odd numbers are included in the same line.

Try
> stem(time,scale=2)

  The decimal point is 1 digit(s) to the right of the |

   3 | 2
   4 | 17
   5 | 09
   6 | 4667789
   7 | 38
   8 | 3
   9 | 0335
  10 | 00
  11 | 0


ignacio

-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Jose A. Hernandez Sent: Monday, March 21, 2005 9:15 AM
To: r-help@stat.math.ethz.ch
Subject: [R] Bug on the stem function or in my brain ?

Good day R-ers!

I was running the basic statistics for the exam that my students took last week and something does not make sense with the stem() fucntion.

Here are two of my variables:

time, is time to complete the exam in minutes exam.1, is the grade for the exam

In stem(), to the left of the vertical bar are the leading digits of the grades. To the right of the vertical bar are the last digits of the grades. Each single digit on the right represents one grade.

> time

  [1] 32 41 47 50 59 64 66 66 67 67 68 69 73 78 83 90 93 93 95
[20] 100 100 110
> stem(time)

   The decimal point is 1 digit(s) to the right of the |

    2 | 2
    4 | 1709
    6 | 466778938
    8 | 30335
   10 | 000

The stem and leaf plot does not reflect the actual data, the bottom line for instance says there were 3 people that spent 100 minutes working on the test. The next to bottom line says there were one 80, three 83s, one 85. And so forth.

> exam.1

  [1] 82 100 86 81 88 78 92 23 91 49 97 9 89 78 93 60 80 80 83
[20] 94 51 100

> stem(exam.1)

   The decimal point is 1 digit(s) to the right of the |

    0 | 9
    2 | 3
    4 | 91
    6 | 088
    8 | 0012368912347
   10 | 00

The Stem-and-Leaf plots DO NOT correspond to the data.

Any educational insights on this issue would be appreciated.

Regards,

Jose

> class(exam.1)
[1] "numeric"
> class(time)

[1] "numeric"

> version

          _
platform i386-pc-mingw32

arch     i386
os       mingw32

system i386, mingw32
status
major 2
minor 0.1
year 2004
month 11
day 15
language R
-- 
Jose A. Hernandez
Ph.D. Candidate
Precision Agriculture Center

Department of Soil, Water, and Climate
University of Minnesota
1991 Upper Buford Circle
St. Paul, MN 55108

Ph. (612) 625-0445, Fax. (612) 625-2208

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Received on Tue Mar 22 03:46:17 2005

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