Jean-Baptiste Rudant wrote:

Hello,

I like to use record arrays to access fields by their name, and because they are esay to use with pytables. But I think it's not very effiicient for what I have to do. Maybe I'm misunderstanding something.

Example :

import numpy as np

age = np.random.randint(0, 99, 10e6)

weight = np.random.randint(0, 200, 10e6)

data = np.rec.fromarrays((age, weight), names='age, weight')

# the kind of operations I do is :

data.age += data.age + 1

# but it's far less efficient than doing :

age += 1

# because I think the record array stores [(age_0, weight_0) ...(age_n, weight_n)]

# and not [age0 ... age_n] then [weight_0 ... weight_n].

Sorry I am not able to answer your question; I am really a new user of numpy also.

It does seem the addition operation is more than 4 times slower, when using record arrays, based on the following:

>>> import numpy, sys, timeit
>>> sys.version
'2.5.2 (r252:60911, Feb 21 2008, 13:11:45) [MSC v.1310 32 bit (Intel)]'
>>> numpy.__version__
'1.2.1'
>>> count = 10e6
>>> ages = numpy.random.randint(0,100,count)
>>> weights = numpy.random.randint(1,200,count)
>>> data = numpy.rec.fromarrays((ages,weights),names='ages,weights')
>>>
>>> timer = timeit.Timer('data.ages += 1','from __main__ import data')
>>> timer.timeit(number=100)
30.110649537860262
>>>
>>> timer = timeit.Timer('ages += 1','from __main__ import ages')
>>> timer.timeit(number=100)
6.9850710076280507
>>>

So I think I don't use record arrays for the right purpose. I only need something which would make me esasy to manipulate data by accessing fields by their name.

Am I wrong ? Is their something in numpy for my purpose ? Do I have to implement my own class, with something like :

class FieldArray:

   def __init__(self, array_dict):

   self.array_list = array_dict



   def __getitem__(self, field):

   return self.array_list[field]



   def __setitem__(self, field, value):

   self.array_list[field] = value



my_arrays = {'age': age, 'weight' : weight}

data = FieldArray(my_arrays)

data['age'] += 1

Thank you for the help,

Jean-Baptiste Rudant
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