Numpy 忽略负值和极值

triples = numpy.arange(0, len(close), 3)
print "Triples", triples[:10], "..."

signs = numpy.ones(len(close))
print "Signs", signs[:10], "..."

signs[triples] = -1
print "Signs", signs[:10], "..."

ma_log = numpy.ma.log(close * signs)
print "Masked logs", ma_log[:10], "..."

Triples [ 0 3 6 9 12 15 18 21 24 27] ...
Signs [ 1. 1. 1. 1. 1. 1. 1. 1. 1. 1.] ...
Signs [-1. 1. 1. -1. 1. 1. -1. 1. 1. -1.] ...
Masked logs [-- 5.93655586575 5.95094223368 -- 5.97468290742
5.97510711452 --
 6.01674381162 5.97889061623 --] ...

dev = close.std()
avg = close.mean()
inside = numpy.ma.masked_outside
  (close, avg - dev, avg + dev)
print "Inside", inside[:10], "..."

Inside [-- -- -- -- -- -- 409.429675172 
        410.240597855 -- --] ...