How to show a dictionary sorted on a value within its data?

Joel Goldstick joel.goldstick at gmail.com
Wed Oct 1 12:56:57 CEST 2014


On Wed, Oct 1, 2014 at 6:45 AM,  <cl at isbd.net> wrote:
> Peter Otten <__peter__ at web.de> wrote:
>> cl at isbd.net wrote:
>>
>> > I have a dictionary as follows:-
>> >
>> > {
>> > u'StarterAmps1': Row(id=4, ain=u'AIN3', name=u'StarterAmps1',
>> > conv=6834.374834509803, Description=u'Starter Amps'), u'LeisureVolts':
>> > Row(id=1, ain=u'AIN0', name=u'LeisureVolts', conv=29.01374215995874,
>> > Description=u'Leisure Volts'), u'RudderPos': Row(id=6, ain=u'AIN5',
>> > name=u'RudderPos', conv=0.028125, Description=u'Rudder Position'), u'xx':
>> > Row(id=7, ain=u'AIN6', name=u'xx', conv=0.028125, Description=u''),
>> > u'LeisureAmps1': Row(id=3, ain=u'AIN2', name=u'LeisureAmps1',
>> > conv=32.727273081945, Description=u'Leisure Amps'), u'StarterVolts':
>> > Row(id=2, ain=u'AIN1', name=u'StarterVolts', conv=28.94469628911757,
>> > Description=u'Starter Volts') }
>> >
>> > I want to output a menu to a user comprising some parts of the
>> > dictionary (ain and Description) sorted by ain.
>> >
>> > Is there some incantation of sorted() that will do what I want?  I
>> > can't quite fathom out the 'key=' parameter needed to sort it by the
>> > tuple item.  Maybe I need a cmp= ?
>> >
>> > E.g. I want to do something like:-
>> >
>> >     for meas in sorted(adc.cfg, key=???):
>> >         print(adc.cfg[meas].ain, adc.cfg[meas].Description)
>> >
>> > What's needed in the ???
>>
>> for meas in sorted(adc.cfg, key=lambda key: adc.cfg[key].ain):
>>     print(adc.cfg[meas].ain, adc.cfg[meas].Description)
>>
> Brilliant, worked perfectly, thank you.  The bit I didn't understamd was
> that 'lambda' bit, but I just looked it up and I'm a bit clearer now.
>
>> or simpler
>>
>> for row in sorted(adc.cfg.values(), key=operator.attrgetter("ain"))
>>     print(row.ain, row.Description)
>>
> I tried this, I got:-
>
>     Traceback (most recent call last):
>       File "/home/chris/bin/calibrate.py", line 24, in <module>
>           for meas in sorted(adc.cfg.values,
>           key=operator.attrgetter("ain")):
>           NameError: name 'operator' is not defined
> I must admit that it's the bits like 'operator' in the parameters that
> I can't really understand where they come from.
>

operator is a module. See
https://docs.python.org/2/library/operator.html#module-operator
>
>> or even
>>
>> for row in sorted(
>>         map(operator.attrgetter("ain", "Description"), adc.cfg.values())):
>>     print(*row)
>>
>
> --
> Chris Green
> ·
> --
> https://mail.python.org/mailman/listinfo/python-list



-- 
Joel Goldstick
http://joelgoldstick.com



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