On Sunday, January 10, 2016 at 7:16:23 AM UTC+5:30, Robert wrote:
> Hi,
>
> I see below code snippet. The return line is not as the usual type.
>
>
>
> def make_cov(cov_type, n_comp, n_fea):
> mincv = 0.1
> rand = np.random.random
> return {
> 'spherical': (mincv + mincv * np.dot(rand((n_components, 1)),
> np.ones((1, n_features)))) ** 2,
> 'tied': (make_spd_matrix(n_features)
> + mincv * np.eye(n_features)),
> 'diag': (mincv + mincv * rand((n_components, n_features))) ** 2,
> 'full': np.array([(make_spd_matrix(n_features)
> + mincv * np.eye(n_features))
> for x in range(n_components)])
> }[cov_type]
>
> Specifically, could you explain the meaning of
>
> {
> ... }[cov_type]
>
> to me?
>
>
> Thanks,
May help if you see it in pseudo-C like this
switch (cov_type)
case 'spherical': return (mincv + mincv * np.dot(rand((n_components, 1)),
np.ones((1, n_features)))) ** 2,
case 'tied': return (make_spd_matrix(n_features)
+ mincv * np.eye(n_features)),
case 'diag': return (mincv + mincv * rand((n_components, n_features)))
** 2,
case 'full': return np.array([(make_spd_matrix(n_features)
+ mincv * np.eye(n_features))
for x in range(n_components)])
Yeah looks backward in python compared to the C-ish
The python is more powerful however because its *data-driven*
ie what is code in C is data in python.
BTW this is one of the motley components collected together under the somewhat
inept moniker of 'functional programming':
http://blog.languager.org/2012/10/functional-programming-lost-booty.html
Also you can make the python look less backward by naming the dictionary,
separate from the lookup:
d = {'spherical' : ..., 'tied' :..., 'diag' : ...}
return d[cov_type]
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