min/max of a mixed type list

[sneekula]

I took a mixed type list and set out to find the min and max values. The results are very surprising to me:

mixed_list = [11, 'Dick', 12, 'Mary', 7, 'Zoe', 9, 700, 777, 'Paul', 13456789]
mn = min(mixed_list)
mx = max(mixed_list)
print mn, type(mn)  # 7 <type 'int'>
print mx, type(mx)  # Zoe <type 'str'>

How does Python handle mixed type lists to get such a result?

[woooee]

How does Python handle mixed type lists to get such a result?

Pretty much, all pc's use ascii encoding and sort in "ascii order", see http://www.asciitable.com/

[mawe]

I took a mixed type list and set out to find the min and max values.

What results have you expected? Is "Dick" larger than 12 or smaller? (I mean the string "Dick", ... :)).
Here's what the docu says:

Note that comparing objects of different types is legal. The outcome is deterministic but arbitrary: the types are ordered by their name. Thus, a list is always smaller than a string, a string is always smaller than a tuple, etc. Mixed numeric types are compared according to their numeric value, so 0 equals 0.0, etc.

And in a footnote:

The rules for comparing objects of different types should not be relied upon; they may change in a future version of the language.

[sneekula]

Thanks mawe,

originally I thought it was by ascii value, but then 11 would have been the min value since ascii 1 is lower than ascii 7. So the order in the list was more like: [7, 9, 11, 12, 700, 777, 13456789, 'Dick', 'Mary', 'Paul', 'Zoe'] Is there a way to get a min/max of each type?

[mawe]

Well, here's the first thing that came to my mind:

In [17]: lst = [5, "Paul", 4, 2, "Mary", 1, "Dick", "Zoe", 3]
In [18]: min_num = min( i for i in lst if isinstance(i, int) )

In [19]: min_str = min( i for i in lst if isinstance(i, str) )

In [20]: min_num
Out[20]: 1

In [21]: min_str
Out[21]: 'Dick'

It works, but there must be something more clever. I'll think about it ...

[woooee]

originally I thought it was by ascii value, but then 11 would have been the min value since ascii 1 is lower than ascii 7.

11 is only less than 7 on the planet Bizarro, and any number AFAIK is sorted before letters so they are all first, because any digit is less than any character. Note that there is a difference between 11 (decimal 11) and '11' (decimal 49, decimal 49) and they will be sorted differently.

[ghostdog74]

I took a mixed type list and set out to find the min and max values. The results are very surprising to me:

mixed_list = [11, 'Dick', 12, 'Mary', 7, 'Zoe', 9, 700, 777, 'Paul', 13456789]
mn = min(mixed_list)
mx = max(mixed_list)
print mn, type(mn)  # 7 <type 'int'>
print mx, type(mx)  # Zoe <type 'str'>

How does Python handle mixed type lists to get such a result?

another way...but you have to test it in different cases...

lst = [11, 'Dick', 12, 'Mary', 7, 'Zoe', 9, 700, 777, 'Paul', 13456789]
slist = sorted(lst) #sort the list
min_num , max_str = slist[0],  slist[-1]  #first and last element usually is minnum, max str.
for num,item in enumerate(slist):
  try:
    if item.isalpha():  #check for first occurence of a word.
      min_str = item
      max_num = slist[num-1]  #get the number on the left of this word. Usually is max num
      break
  except: pass
print min_num ,max_num , max_str ,  min_str

[vegaseat]

If a sort would be purely by ASCII value then you would have to treat the list elements as strings ...

# convert all list items to type string ...
mixed_list = [11, 'Dick', 12, 'Mary', 7, 'Zoe', 9, 700, 777, 'Paul', 13456789]
str_list = [str(x) for x in mixed_list]
# now it's a pure ASCII sort ...
print sorted(str_list)
"""
output -->
['11', '12', '13456789', '7', '700', '777', '9', 'Dick', 'Mary', 'Paul', 'Zoe']
"""

I think that was what Sneekula originally though might have happened.

I leaned on mawe's idea and created a generic function to extract the min and max values of a given type from a mixed list ...

def minmax4(lst, typ):
    """return min/max of mixed list lst for items of type typ"""
    temp = [x for x in lst if isinstance(x, typ)]
    return min(temp), max(temp)
 
# minmax4() test ...
mixed_list = [11, 'Dick', 12, 'Mary', 7, 'Zoe', 9, 700, 777, 'Paul', 13456789]
print mixed_list
 
print "The min and max of the integers are:"
mn, mx = minmax4(mixed_list, int)
print "minimum = %s  maximum = %s" % (mn, mx)
 
print "The min and max of the strings are:"
mn, mx = minmax4(mixed_list, str)
print "minimum = %s  maximum = %s" % (mn, mx)
"""
minmax4() test output -->
[11, 'Dick', 12, 'Mary', 7, 'Zoe', 9, 700, 777, 'Paul', 13456789]
The min and max of the integers are:
minimum = 7  maximum = 13456789
The min and max of the strings are:
minimum = Dick  maximum = Zoe
"""