Logarithmic scales about flot HOT 23 OPEN

Are we talking about logarithmic scales here? The automatic stuff in Flot can't 
do it
at the moment, but it shouldn't be too hard to prescale the values and provide 
ticks
yourself.

i've made a quick implementation of logarithmic scales on y axis
I'think that this match the requirements

I'm working on modified flot version downloaded from Issue #5
you can see the code in attach

to use logarithmic scale set  yaxis:{logarithmicScale:true} in options

questions are welcome

Something happened with the attachment. Would you mind creating a patch against 
SVN?
I'm curious as to how many lines of code this requires.

I cannot access SVN here, and in this moment it's hard to make a patch from a 
very
modified version .. 

btw logarithmic Yscale require 6 lines of code

first define option default value (line 47) 
            yaxis: {
                autoscaleMargin: 0.02, logarithmicScale: false
            },

then in processData (insert after line 262) prescale all values to log scale

                    if (options.yaxis.logarithmicScale&& y!=0)
                        data[j][1]=(y=Math.log(y)/Math.log(10));

finally as you said, provide a custom yaxis.tickFormatter (in parseOptions 
before
line 150)
            if (options.yaxis.logarithmicScale)
                options.yaxis.tickFormatter=function(n, axis) 
                {return Math.pow(10,n).toFixed(axis.tickDecimals);}

I've just released version 0.5 so it should be easier now.

I think it makes sense to have logarithmic: null or number instead of just
true/false, otherwise I'm going to get spammed by people wanting to use log 
base 2 or
log base e.

Note that the patch must be general enough to work with all four axes (actually 
I
think this is pretty easy to do.

This is very good idea.
I'm looking forward to be included this patch into the main stream.

Hello,

I have added preliminary support for arbitrary bases in axes, you can find it 
on my gitweb:

http://www.leto.net/gitweb/?p=flot.git;a=shortlog;h=refs/heads/leto

Or you can grab it on the command line with:

git clone http://leto.net/code/flot.git 

Here is the example page that I added to the examples/ directory:

http://leto.net/plot/examples/logarithms.html

Any suggestions for improvement are welcome.

Cheers

Here is a patch for logarithmic bases against svn rev 131. Any comments for
refactoring and improvements are welcome.

Cheers

Hi, Correct me if I'm wrong, but I've been messing around with your examples 
and 
noticed that this doesn't account for zooming. Also, if using any type of 
tooltip you 
have to Math.pow(n, value) to get the actual value (which may lead to values 
being 
off). Is there any way around this? Specifically the zooming part.

Thanks
Ben

Hi jaleto,

I've been using your mods from your git for weeks now and found them incredibly 
useful.  I did find one bug.  A logarithmic data value <= 0 passes through the 
code unscaled and is plotted at it's unscaled position.  This 
is a bug, since negative values will show up as some sort of positive value.  
I've fixed so these values are 
nulled out and attached a patch file.  The patch file is diffed against the 
already patched r131 version of 
jquery.flot.js

Thanks!
Chris

Ben is totally correct, the way the patch works is to change the rendering of 
the
ticks on each axis, but tooltips and zooming don't play nice yet. I am thinking 
about
how to best deal with this.

Chris: Thanks for squashing that bug, I really need to write some tests! I will
incorporate your patch and submit a new patch to Ole.

Cheers

there's much more required to implement log scaling.
1. data has to be transformed in processData, but original data has to be 
retained to
pass back when events are fired (plothover, plotclick, etc.)  Just converting 
to log
and then taking the exponent later is lossy so should not be done.

2. The axes have to be logscaled as well, however the ticks have to be 
displayed in
the units of the original data

3. options.?axis.min and max have to be transformed

4. any ticks passed in by the caller have to be transformed

5. custom grid markers have to be transformed


I've done all of the above in a version of flot that I ported to YUI, 
unfortunately,
I cannot provide a diff against the jQuery version because I don't use that 
version,
but in general the changes are identical to the code above, just that you have 
to
apply them to many more places.

FYI, the transform callback in Flot 0.6 should make this much, much easier. I 
think
it would make sense to make a little plugin that wraps it up. We just need a
transform function, intelligent ticks and some error checking. Probably just a
question of porting the above patch.

pillip, can you pretty please port your log thing to jquery flot? It'll make 
webnumbr.com that much cooler :)

Sorry, my ignorance maybe, but I don't seem to get the transform callback 
option to
work properly because I pass *all* my data in JSON. I mean, I can't explicitely 
pass

xaxis: {
    transform: function (v) { return Math.log(v); },
    inverseTransform: function (v) { return Math.exp(v); }
  }

but all I can pass to flot is

xaxis: {
    transform: "function (v) { return Math.log(v); }",
    inverseTransform: "function (v) { return Math.exp(v); }"
  }

(unless I would add a layer when I import my JSON to "revive" the functions in 
the
JSON, if any)

Or is there a logarithmic scale plugin available? (didn't find one under the 
plugins
page).
[[and by the way I'm a huge fan of flot -- thanks for a very nice app]]

It it correct that zooming and tooltips are still problematic when using the 
transform/inverseTransform functions?  

I'm using a transform in order to display stock data over multiple weeks 
(hiding the weekend days), but anything past the first weekend fails to render 
when zoomed, and won't show tooltips on the datapoints.

Hi,
One piece of data that I charted recently showed all the points on a Y scale of 
about 0 to 50, but there is one point which hits 3000. Because of this, when I 
look at the chart I cant really see the trends of most data because it gets 
scaled down. Is there any way to have dynamic Y axis, where it would conform 
evenly to 90% (or variable percentage) of data, and the rest to be shown out of 
proportion. And the grid lines could change to reflect it.
Something like this:

http://www.jqplot.com/tests/logAxisTests.php

Your help much appreciated

hi!
I've been struggling with log scales as well!
Actually, I'm really not an expert in javascript, I'm not even a professional 
programmer, but I found flot as been so useful for my needs!
Would you please help me in fixing the crosshair/tooltip with log scale? I 
think the visualization now is correct, but I can get the tooltip to catch the 
points in the plot! What should I do?
PS: any other comment on my crappy code is expected :D

Thanks

The instructions on comment #15 works correctly  (at least for y axis), 
including zoom and pan using the navigation plugin, and with correct 
informations form plothover/click events.

I haven't tested it on xaxis, cause i don't need a log-log plot, but only a 
vertical log scale.

However, pay attention if your yaxis goes to 0, since log(0) is negative 
infinity, it causes errors inside flot (it would be nice if flot could report 
this errors, like invalid values returned from the transform function, instead 
of simply forwarding the innermost canvas error, which does not say a lot). 

I decided to return log(0.0001) for zero (it's more or less -10), and have no 
data series that goes negative, so I don't handle them.

So, this works for me :

options.yaxis = {
  transform: function (v) {
    if (v == 0) v = 0.0001;
    return Math.log(v);
  },
  inverseTransform: function (v) { return Math.exp(v); }
};

I read all the comments in this issue and i still cant draw log-log graph can 
you provide me by example 

why the transform functions wont be {
  transform: function (v) {
    Math.pow(10,v);
  },
  inverseTransform: function (v) { return Math.log(v)/Math.log(10); }
};

Wanted to follow up on this Enhancement request.
So far I've found that the modified code provided in the 2nd comment does it's 
job well and have modified it myself a bit more in order to allow for both axis 
to use the logarithmic scale as I need for both axis to use said scale.

Any chance this enhancement can be ported to the latest version?

The graph I'm working on can be found here http://irken.codebeta.net/plot.php

The recent move of time-axis support into its own plugin is an excellent 
example for a log-axis plugin.