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Re: st: Re: Stack trick by Nicholas Cox
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: Re: Stack trick by Nicholas Cox
Date
Mon, 4 Mar 2013 20:17:33 +0000
I see. I gave you two ways of doing something similar with single commands.
Nick
On Mon, Mar 4, 2013 at 8:10 PM, Michael Stewart
<[email protected]> wrote:
> Thanks a lot for clarification.
> I dont have specific task in mind but I was just commenting on the
> utility of the set of commands written by you for the stack trick
> Thanks again
> Mike
>
> On Mon, Mar 4, 2013 at 2:49 PM, Nick Cox <[email protected]> wrote:
>> Thanks, not quite sure which specific task(s) you have in mind. But consider
>>
>> sysuse auto
>> logit foreign mpg
>> regplot, jitter(1)
>>
>> predict predicted
>> stripplot mpg, over(foreign) stack height(0.2) addplot(mspline
>> predicted mpg, bands(100))
>>
>> where -regplot- is from SJ and -stripplot- is from SSC.
>>
>> Nick
>>
>> On Mon, Mar 4, 2013 at 7:33 PM, Michael Stewart
>> <[email protected]> wrote:
>>> Thanks a lot for such a nice explanation and taking time to type explain it.
>>> I understand it now.
>>> These are such a nice set of commands & are extremely useful, I hope
>>> one of the experienced stata programmers out there could write a user
>>> written program for it .!!
>>> Thanks a lot Nick
>>> Mike
>>>
>>>
>>> On Mon, Mar 4, 2013 at 4:50 AM, Nick Cox <[email protected]> wrote:
>>>> The reference is to a Speaking Stata column in the _Stata Journal_.
>>>> This is accessible to all in
>>>>
>>>> http://stata-journal.com/sjpdf.html?articlenum=gr0004
>>>>
>>>> The example uses Stata's auto data and can be replicated by
>>>>
>>>> sysuse auto
>>>>
>>>> bysort foreign mpg: gen foreign2 = ///
>>>> cond(foreign==1, 1-0.1*(_n-1)/7, foreign+0.1* (_n-1)/7)
>>>>
>>>> The results can be inspected. Here is enough to give a flavour of what
>>>> is produced
>>>>
>>>> . l foreign mpg foreign2
>>>>
>>>> +---------------------------+
>>>> | foreign mpg foreign2 |
>>>> |---------------------------|
>>>> 1. | Domestic 12 0 |
>>>> 2. | Domestic 12 .0142857 |
>>>> 3. | Domestic 14 0 |
>>>> 4. | Domestic 14 .0142857 |
>>>> 5. | Domestic 14 .0285714 |
>>>> |---------------------------|
>>>> 6. | Domestic 14 .0428571 |
>>>> 7. | Domestic 14 .0571429 |
>>>> 8. | Domestic 15 0 |
>>>> 9. | Domestic 15 .0142857 |
>>>>
>>>> <snip>
>>>>
>>>> 53. | Foreign 14 1 |
>>>> 54. | Foreign 17 1 |
>>>> 55. | Foreign 17 .9857143 |
>>>> |---------------------------|
>>>> 56. | Foreign 18 1 |
>>>> 57. | Foreign 18 .9857143 |
>>>> 58. | Foreign 21 1 |
>>>> 59. | Foreign 21 .9857143 |
>>>> 60. | Foreign 23 1 |
>>>> |---------------------------|
>>>> 61. | Foreign 23 .9857143 |
>>>> 62. | Foreign 23 .9714286 |
>>>> 63. | Foreign 24 1 |
>>>> 64. | Foreign 25 1 |
>>>> 65. | Foreign 25 .9857143 |
>>>> |---------------------------|
>>>> 66. | Foreign 25 .9714286 |
>>>> 67. | Foreign 25 .9571428 |
>>>> 68. | Foreign 26 1 |
>>>> 69. | Foreign 28 1 |
>>>> 70. | Foreign 30 1 |
>>>> |---------------------------|
>>>> 71. | Foreign 31 1 |
>>>> 72. | Foreign 35 1 |
>>>> 73. | Foreign 35 .9857143 |
>>>> 74. | Foreign 41 1 |
>>>> +---------------------------+
>>>>
>>>> The idea is to get a y coordinate at which to plot each pair of values
>>>> in a scatter plot of -foreign- versus -mpg-. The context is that we
>>>> are plotting a logit fit from -logit foreign mpg- and we are adding
>>>> the raw data at the top and bottom of the plot as what are now often
>>>> called as rugs.
>>>>
>>>> Consider the last observation, which is the only observation with
>>>> foreign = 1 (Foreign), mpg = 41. We can just plot it as y = 1, x = 41.
>>>>
>>>> The previous two observations tie at foreign = 1, mpg = 35. If we
>>>> plotted them, the marker symbols would just be superimposed.
>>>>
>>>> So we stack them vertically. One can be plotted at y = 1, x = 35, but
>>>> the other must be nudged downwards from y = 1.
>>>>
>>>> A similar decision applies for values with foreign = 0. Pairs that
>>>> occur once only can be plotted at y = 0, x = mpg value, but ties must
>>>> be separated to be discernible.
>>>>
>>>> The general rule for this dataset -- chosen after experiment -- was
>>>>
>>>> cond(foreign==1, 1-0.1*(_n-1)/7, foreign+0.1* (_n-1)/7)
>>>>
>>>> meaning
>>>>
>>>> for foreign = 1, use y = 1 if _n == 1, 1 - 0.1/7 if _n == 2, and so on.
>>>>
>>>> for foreign = 0, use y = 0 if _n == 1, 0 + 0.1/7 if _n == 3, and so on.
>>>>
>>>> The -cond()- function handles both cases at once. -search cond, sj-
>>>> for access to a 2005 tutorial by David Kantor and myself if needed.
>>>>
>>>> What is _n here? It is crucial that the observation number _n is
>>>> counted _within_ distinct groups of -foreign mpg-. -search by, sj- for
>>>> access to a 2002 tutorial if needed.
>>>>
>>>> 7 is just a choice that works well in this dataset, or so I thought.
>>>>
>>>> There is no use of options in this code.
>>>>
>>>> Nick
>>>>
>>>> On Sun, Mar 3, 2013 at 8:10 PM, Michael Stewart
>>>> <[email protected]> wrote:
>>>>
>>>>> I am a novice and trying to learn stata graphics.I read Speaking Stat
>>>>> by Nick, vol 4 , number 2, page 190-215 regarding Graphing Categorical
>>>>> and compositional data.
>>>>> Nick writes a conditional statement on page 193.I could not understand
>>>>> the second option
>>>>> His cond statement is bysort foreign mpg:gen foreign2=cond(foreign==1,
>>>>> 1-0.1*(_n-1)/7, foreign+0.1*(_n-1)/7)
>>>>> I cannot understand what does 1-0.1*(_n-1)/7 and
>>>>> foreign+0.1*(_n-1)/7 compute and their purpose.I tried to read the
>>>>> article but am still at loss.
>>>> *
>>>> * For searches and help try:
>>>> * http://www.stata.com/help.cgi?search
>>>> * http://www.stata.com/support/faqs/resources/statalist-faq/
>>>> * http://www.ats.ucla.edu/stat/stata/
>>>
>>>
>>>
>>> --
>>> Thank you ,
>>> Yours Sincerely,
>>> Mike.
>>> *
>>> * For searches and help try:
>>> * http://www.stata.com/help.cgi?search
>>> * http://www.stata.com/support/faqs/resources/statalist-faq/
>>> * http://www.ats.ucla.edu/stat/stata/
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/faqs/resources/statalist-faq/
>> * http://www.ats.ucla.edu/stat/stata/
>
>
>
> --
> Thank you ,
> Yours Sincerely,
> Mike.
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/faqs/resources/statalist-faq/
> * http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
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