Sorting a List of Objects by an Attribute of the ObjectsCase-Insensitively

[Jason]

Hi folks--

Basically, I have a pressing need for a combination of 5.2 "Sorting a
List of Strings Case-Insensitively" & 5.3 "Sorting a List of Objects
by an Attribute of the Objects" from the Python Cookbook.

My first guess isn't working:

import operator
def sort_by_attr(seq, attr):
key=operator.attrgetter(attr)
key=str.lower
return sorted(seq, key)

....would much appreciate any guidance!

 

[David Harrison]

Hi folks--

Basically, I have a pressing need for a combination of 5.2 "Sorting a
List of Strings Case-Insensitively" & 5.3 "Sorting a List of Objects
by an Attribute of the Objects" from the Python Cookbook.

My first guess isn't working:

import operator
def sort_by_attr(seq, attr):
key=operator.attrgetter(attr)
key=str.lower
return sorted(seq, key)

...would much appreciate any guidance!

You're probably looking for the built-in function sorted,

e.g.

class Foo:
def __init__(self, value):
self.value = value

def __repr__(self):
return self.value

a = [Foo('c'), Foo('B'), Foo('A')]

print sorted(
a,
cmp=lambda x,y: cmp(x.lower(), y.lower()),
key=lambda x: x.value
)

 

[Jason]

Hi folks--

Basically, I have a pressing need for a combination of 5.2 "Sorting a
List of Strings Case-Insensitively" & 5.3 "Sorting a List of Objects
by an Attribute of the Objects" from the Python Cookbook.

My first guess isn't working:

import operator
def sort_by_attr(seq, attr):
key=operator.attrgetter(attr)
key=str.lower
return sorted(seq, key)

...would much appreciate any guidance!

You're probably looking for the built-in function sorted,

e.g.

class Foo:
def __init__(self, value):
self.value = value

def __repr__(self):
return self.value

a = [Foo('c'), Foo('B'), Foo('A')]

print sorted(
a,
cmp=lambda x,y: cmp(x.lower(), y.lower()),
key=lambda x: x.value
)

Hey-- thanks!

I actually figured out something that works quite nicely since I
posted:

def sort_by_attr_case_insensitive(seq, attr):
return sorted(seq, cmp=lambda x,y: cmp(x.lower(), y.lower()),
key=operator.attrgetter(attr))

 

[Paddy]

Hi folks--

Basically, I have a pressing need for a combination of 5.2 "Sorting a
List of Strings Case-Insensitively" & 5.3 "Sorting a List of Objects
by an Attribute of the Objects" from the Python Cookbook.

My first guess isn't working:

import operator
def sort_by_attr(seq, attr):
key=operator.attrgetter(attr)
key=str.lower
return sorted(seq, key)

...would much appreciate any guidance!

HiJason,
Try key= lambda x: x.attr.lower()
The above should calculate the key only once for the items to be
sorted rather than using cmp which calculates more than that.

- Paddy.

 

[Peter Otten]

HiJason,
Try key= lambda x: x.attr.lower()
The above should calculate the key only once for the items to be
sorted rather than using cmp which calculates more than that.

A key func is indeed preferable over cmp. Here is a working example:
.... def __init__(self, name, value):
.... self.name = name
.... self.value = value
.... def __repr__(self):
.... return "%s|%s" % (self.name, self.value)
....

items = [A("a", "z"), A("C", "Y"), A("b", "x")]
items [a|z, C|Y, b|x]
def sorted_by_attr_icase(items, attrname):

.... get = operator.attrgetter(attrname)
.... return sorted(items, key=lambda item: get(item).lower())
....

sorted_by_attr_icase(items, "name") [a|z, b|x, C|Y]
sorted_by_attr_icase(items, "value")

[b|x, C|Y, a|z]

Peter

 

[Jason]

Thanks so much everyone! That works great, & (presumably) is way
faster than the way I was doing it--