Graph Dates and Values
gagsl-py2 at yahoo.com.ar
Tue Mar 10 17:44:41 CET 2009
En Tue, 10 Mar 2009 13:32:10 -0200, brianrpsgt1 <brianlong at cox.net>
> On Mar 10, 7:40 am, "Gabriel Genellina" <gagsl-... at yahoo.com.ar>
>> En Tue, 10 Mar 2009 05:08:41 -0200, brianrpsgt1 <brianl... at cox.net>
>> > I am trying to plot dates and values on a graph using matplotlib.
>> > Below is the code. I can run this and it works great, until I get to
>> > about 2000 rows from the DB. Things really start to slow down. I
>> > have successfully plotted up to 5000 rows from the DB, but it is very
>> > slow. I am attempting to plot values for a day, which would be equal
>> > to 84600 records. Is there a more efficient may to accomplish this?
>> Without looking at the matplotlib docs, the above  suggests that both
>> date2num and plt.plot take a list of values to act upon, and you're
>> feeding one point at a time. Probably you end up creating one series
>> point (instead of a single series with many points). I guess something
>> like this should work:
>> x, y = zip(*value_data) # "transpose"
>> dates = mdates.date2num(x)
>> plt.plot(dates, y, 'bo', ms=6)
> Thanks for the notes. That is exactly what I thought the problem
> was. Here is an update. I put a limit to 100 on the SQL Query to
> test. When I run your code, I get the data returned, however, I get
> the same return equal to the limit I set. In other words, when I run
> with a limit of 100, I get the same result 100 times. Which would
> mean that when I try to run a whole day (86400 :) - it was late!), I
> am getting the same result 86400 times and then it is tyring to plot
> Output below:
> [ 733414.06489583 733414.06490741 733414.06491898 733414.06493056 ...
> 733414.06600694 733414.06601852 733414.06603009 733414.06604167]
> (95, 95, 95, 95, ... 95, 95, 95, 94)
> If I run this code:
> for s in value_data:
> x = mdates.date2num([s])
> y = [s]
> print [x, y]
> The results returned are the following:
> There are 100 rows in the database
> [ 733414.06489583] 
> [ 733414.06490741] 
> [ 733414.06491898] 
> [ 733414.06493056]  ...
> [ 733414.06600694] 
> [ 733414.06601852] 
> [ 733414.06603009] 
> [ 733414.06604167] 
Well, both look the same values to me... what's wrong? Why do you say "the
same results 100 times".
Oh, the code fragment I posted is suposed to *replace* the original for
loop. Don't put it inside a loop.
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