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AW: st: Can you confirm these Stata limitations?


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   AW: st: Can you confirm these Stata limitations?
Date   Tue, 7 Sep 2010 17:56:37 +0200

<> 
"1. Not true

set obs 100
forv i=1(1)100 {
gen x`i'=uniform()
}
gen id=round(_n/10)
collapse x*, by(id)"




For a plain-vanilla -varlist- w/o factor variables, the upper limit seems to
be quite high. I guess it is limited only by the  # of variables which is
32,767 for my Stata MP. Also note you have to tell Stata the maximum # of
vars via -set maxvar-. This code runs in 100 seconds for me:

*************
clear*
set maxvar 3500
set obs 100

foreach var of newlist x1-x3000{
	gen `var'=runiform()
}

gen id=round(_n/10)

collapse x*, by(id)
*************



HTH
Martin


-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Jorge Eduardo
Pérez Pérez
Gesendet: Dienstag, 7. September 2010 16:14
An: statalist@hsphsun2.harvard.edu
Betreff: Re: st: Can you confirm these Stata limitations?

1. Not true

set obs 100
forv i=1(1)100 {
gen x`i'=uniform()
}
gen id=round(_n/10)
collapse x*, by(id)

2. See -cond-


_______________________
Jorge Eduardo Pérez Pérez




On Sun, Sep 5, 2010 at 2:26 PM, Pietro Mazzoni <pm125@columbia.edu> wrote:
> Hello everyone,
>
> It's my first time writing to this list, which is a very helpful forum. I
can use some help in clarifying certain features of Stata that seem to be
limitations, at least in the style of analysis I would like to implement. I
am deciding whether to have my whole lab switch from JMP to Stata for our
data analysis due to the high cost of JMP. I will avoid the debate about
virtues and faults of an interactive, GUI-based program like JMP. I see the
value and power of Stata's approach, and cost considerations may be forcing
us to switch regardless. But the following limitations are making it
difficult to convince my postdocs (and, frankly, me), that using Stata will
not, even after a transition period, take orders of magnitude more time for
visualization of our data. I apologize if these questions are elementary. I
read through "A Gentle Introduction to Stata" and searched the Web, but
could not find these answers.
>
> I am using Stata 10 for Mac. The data is usually a table of movement
variables (duration, peak velocity, etc) for each of several trials in motor
control experiments. There are several trials per condition, several
conditions per session, a few sessions per subject, and several subjects per
group. We usually work with two main tables: the one just described (to look
at trial-to-trial time course of variables within conditions) and a
calculated table that has the mean values of all these variables for each
condition.
>
> 1. A common step early in our analysis is to collapse single-trial data
into mean values per condition. Is it indeed true that the collapse command
can only handle 8 variables at a time? This means that instead of being able
to create a single table with all the variables' means, I'd have to create
multiple tables, 8 variables at a time, and then join them.
>
> 2. We often calculate derived variables based on a formula. However, the
formula can differ slightly for different groups or conditions. Can a
complex "if" statement be used at the end of a formula, or is there the
equivalent of a "case..." command that could be part of a formula. For
example:
>
> gen int outcome = [ 1 if (peakVel > 10 & condition == "easy"); 2 if
(peakVel > 50 & condition == "difficult") ]
>
> 3. Is it true that there is no option for error bars in a continuous vs.
categorical plot, i.e. it is necessary to convert the category into a
numerical variable in order to plot error bars? I found the command serrbar,
which removes some of the steps required in the usual workarounds
(calculating error value is enough; high and low values are no longer
explicitly needed), but it only works with a continuous-variable x axis.
This is a minor inconvenience (the much more lamented inconvenience, for
users of JMP, is not being able to have the graph show standard error on a
mean plot without having to explicitly calculate it).
>
> 4. Is there any way to create a graph that shows individual values
overlaid on top of mean values? For example, one that has the following two
elements on a single graph, for variables vel, subj, group (one value of vel
for each subj; several subj per group; several groups):
>
> a.  vel vs. group: individual values of vel (one value for each subject)
as dots lined up as a vertical array above each condition
> b. group mean of vel vs. group: mean values of vel, across each group,
indicated by a bar or a thick orizontal marker, aligned with the vertical
array of dots above each condition.
>
> This graph is of common use for our data: it allows us to see mean values
of a variable for a group while at the same time seeing how that mean arises
from individual subject values.
>
> 5. The time it takes for Stata 10 to generate a graph on a Mac, even on a
late-model machine, is inordinately slow (several seconds) and grows quickly
(to tens of seconds) with the number of elements that are added to the
graph. Does anyone know if Stata 11 is faster at drawing graphs on a Mac?
>
> Thank you in advance for any uelp or suggestions.
>
> Pietro
> -----------------------
> Pietro Mazzoni, MD PhD
> Associate Professor of Neurology
> Co-director, Motor Performance Laboratory
> Columbia University
> New York
>
>
>
>
>
> *
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> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>

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