Programmatically finding "significant" data points

[Paul McGuire]

"robert" <no-spam at no-spam-no-spam.invalid> wrote in message 
news:ejpf2r$p8g$1 at news.albasani.net...
> erikcw wrote:
>> Hi all,
>>
>> I have a collection of ordered numerical data in a list.  The numbers
>> when plotted on a line chart make a low-high-low-high-high-low (random)
>> pattern.  I need an algorithm to extract the "significant" high and low
>> points from this data.
>>
>> Here is some sample data:
>> data = [0.10, 0.50, 0.60, 0.40, 0.39, 0.50, 1.00, 0.80, 0.60, 1.20,
>> 1.10, 1.30, 1.40, 1.50, 1.05, 1.20, 0.90, 0.70, 0.80, 0.40, 0.45, 0.35,
>> 0.10]
>>
>> In this data, some of the significant points include:
>> data[0]
>> data[2]
>> data[4]
>> data[6]
>> data[8]
>> data[9]
>> data[13]
>> data[14]
>> ....
>>
>> How do I sort through this data and pull out these points of
>> significance?

Using zip and map, it's easy to compute first and second derivatives of a 
time series of values.  The first lambda computes