Define dtypes in NumPy using a list?

numpy, python

Solution

The following code might help:

import numpy as np

dt = np.dtype([('name1', '|S10'), ('name2', '<f8')])
tuplelist=[
    ('n1', 1.2),
    ('n2', 3.4),    
     ]
arr = np.array(tuplelist, dtype=dt)

print(arr['name1'])
# ['n1' 'n2']
print(arr['name2'])
# [ 1.2  3.4]

Your immediate problem was that `np.dtype` expects the format specifiers to be numpy types, such as `'|S10'` or `'<f8'` and not Python types, such as `str` or `float`. If you type `help(np.dtype)` you'll see many examples of how `np.dtypes` can be specified. (I've only mentioned a few.)

Note that np.array expects a list of tuples. It's rather particular about that.

A list of lists raises `TypeError: expected a readable buffer object`.

A (tuple of tuples) or a (tuple of lists) raises `ValueError: setting an array element with a sequence`.

Problem

I just am having a problem with NumPy dtypes. Essentially I'm trying to create a table that looks like the following (and then save it using rec2csv): ``` name1 name2 name3 . . . name1 # # # name2 # # # name2 # # # . . . ``` The matrix (numerical array in the center), is already computed before I attempt to add the name tags. I've tried to use the following code: ``` dt = dtype({'names' : tuple(blah), 'formats' : tuple(fmt)}) ReadArray = array(tuplelist, dtype=dt) ``` where tuplelist is a list of rows (i.e. the row [name1, #, #, #...]), blah is a list of strings (i.e. the names, `blah = ['name1', 'name2', ...]`) and fmt is the list of format,s (i.e. `fmt = [str, float, float, ...]`). The error I'm getting is the following: ``` Traceback (most recent call last): File "<stdin>", line 1, in <module> File "table_calc_try2.py", line 152, in table_calc_try2 dt = dtype({'names' : tuple(blah), 'formats' : tuple(fmt)}) TypeError: data type not understood ``` Can anyone help? Thanks!

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