Given [1,2,3,4,5]
, how can I do something like
1/1, 1/2, 1/3,1/4,1/5, ...., 3/1,3/2,3/3,3/4,3/5,.... 5/1,5/2,5/3,5/4,5/5
I would like to store all the results, find the minimum, and return the two numbers used to find the minimum. So in the case I've described above I would like to return (1,5)
.
So basically I would like to do something like
for each element i
in the list
map some function across all elements in the list, taking i
and j
as parameters
store the result in a master list, find the minimum value in the master list, and return the arguments i
, j
used to calculate this minimum value.
In my real problem I have a list objects/coordinates, and the function I am using takes two coordinates and calculates the euclidean distance. I'm trying to find minimum euclidean distance between any two points but I don't need a fancy algorithm.
This question is related to
python
algorithm
list
list-comprehension
Some readable python:
def JoeCalimar(l):
masterList = []
for i in l:
for j in l:
masterList.append(1.*i/j)
pos = masterList.index(min(masterList))
a = pos/len(masterList)
b = pos%len(masterList)
return (l[a],l[b])
Let me know if something is not clear.
>>> nums = [1, 2, 3, 4, 5]
>>> min(map((lambda t: ((float(t[0])/t[1]), t)), ((x, y) for x in nums for y in nums)))[1]
(1, 5)
If you don't mind importing the numpy package, it has a lot of convenient functionality built in. It's likely to be much more efficient to use their data structures than lists of lists, etc.
from __future__ import division
import numpy
data = numpy.asarray([1,2,3,4,5])
dists = data.reshape((1,5)) / data.reshape((5,1))
print dists
which = dists.argmin()
(r,c) = (which // 5, which % 5) # assumes C ordering
# pick whichever is most appropriate for you...
minval = dists[r,c]
minval = dists.min()
minval = dists.ravel()[which]
Doing it the mathy way...
nums = [1, 2, 3, 4, 5]
min_combo = (min(nums), max(nums))
Unless, of course, you have negatives in there. In that case, this won't work because you actually want the min and max absolute values - the numerator should be close to zero, and the denominator far from it, in either direction. And double negatives would break it.
If working with Python =2.6 (including 3.x), you can:
from __future__ import division
import operator, itertools
def getmin(alist):
return min(
(operator.div(*pair), pair)
for pair in itertools.product(alist, repeat=2)
)[1]
getmin([1, 2, 3, 4, 5])
EDIT: Now that I think of it and if I remember my mathematics correctly, this should also give the answer assuming that all numbers are non-negative:
def getmin(alist):
return min(alist), max(alist)
Doing it the mathy way...
nums = [1, 2, 3, 4, 5]
min_combo = (min(nums), max(nums))
Unless, of course, you have negatives in there. In that case, this won't work because you actually want the min and max absolute values - the numerator should be close to zero, and the denominator far from it, in either direction. And double negatives would break it.
Some readable python:
def JoeCalimar(l):
masterList = []
for i in l:
for j in l:
masterList.append(1.*i/j)
pos = masterList.index(min(masterList))
a = pos/len(masterList)
b = pos%len(masterList)
return (l[a],l[b])
Let me know if something is not clear.
If I'm correct in thinking that you want to find the minimum value of a function for all possible pairs of 2 elements from a list...
l = [1,2,3,4,5]
def f(i,j):
return i+j
# Prints min value of f(i,j) along with i and j
print min( (f(i,j),i,j) for i in l for j in l)
If you don't mind importing the numpy package, it has a lot of convenient functionality built in. It's likely to be much more efficient to use their data structures than lists of lists, etc.
from __future__ import division
import numpy
data = numpy.asarray([1,2,3,4,5])
dists = data.reshape((1,5)) / data.reshape((5,1))
print dists
which = dists.argmin()
(r,c) = (which // 5, which % 5) # assumes C ordering
# pick whichever is most appropriate for you...
minval = dists[r,c]
minval = dists.min()
minval = dists.ravel()[which]
Doing it the mathy way...
nums = [1, 2, 3, 4, 5]
min_combo = (min(nums), max(nums))
Unless, of course, you have negatives in there. In that case, this won't work because you actually want the min and max absolute values - the numerator should be close to zero, and the denominator far from it, in either direction. And double negatives would break it.
Some readable python:
def JoeCalimar(l):
masterList = []
for i in l:
for j in l:
masterList.append(1.*i/j)
pos = masterList.index(min(masterList))
a = pos/len(masterList)
b = pos%len(masterList)
return (l[a],l[b])
Let me know if something is not clear.
If I'm correct in thinking that you want to find the minimum value of a function for all possible pairs of 2 elements from a list...
l = [1,2,3,4,5]
def f(i,j):
return i+j
# Prints min value of f(i,j) along with i and j
print min( (f(i,j),i,j) for i in l for j in l)
If working with Python =2.6 (including 3.x), you can:
from __future__ import division
import operator, itertools
def getmin(alist):
return min(
(operator.div(*pair), pair)
for pair in itertools.product(alist, repeat=2)
)[1]
getmin([1, 2, 3, 4, 5])
EDIT: Now that I think of it and if I remember my mathematics correctly, this should also give the answer assuming that all numbers are non-negative:
def getmin(alist):
return min(alist), max(alist)
If I'm correct in thinking that you want to find the minimum value of a function for all possible pairs of 2 elements from a list...
l = [1,2,3,4,5]
def f(i,j):
return i+j
# Prints min value of f(i,j) along with i and j
print min( (f(i,j),i,j) for i in l for j in l)
If working with Python =2.6 (including 3.x), you can:
from __future__ import division
import operator, itertools
def getmin(alist):
return min(
(operator.div(*pair), pair)
for pair in itertools.product(alist, repeat=2)
)[1]
getmin([1, 2, 3, 4, 5])
EDIT: Now that I think of it and if I remember my mathematics correctly, this should also give the answer assuming that all numbers are non-negative:
def getmin(alist):
return min(alist), max(alist)
If I'm correct in thinking that you want to find the minimum value of a function for all possible pairs of 2 elements from a list...
l = [1,2,3,4,5]
def f(i,j):
return i+j
# Prints min value of f(i,j) along with i and j
print min( (f(i,j),i,j) for i in l for j in l)
Some readable python:
def JoeCalimar(l):
masterList = []
for i in l:
for j in l:
masterList.append(1.*i/j)
pos = masterList.index(min(masterList))
a = pos/len(masterList)
b = pos%len(masterList)
return (l[a],l[b])
Let me know if something is not clear.
>>> nums = [1, 2, 3, 4, 5]
>>> min(map((lambda t: ((float(t[0])/t[1]), t)), ((x, y) for x in nums for y in nums)))[1]
(1, 5)
If you don't mind importing the numpy package, it has a lot of convenient functionality built in. It's likely to be much more efficient to use their data structures than lists of lists, etc.
from __future__ import division
import numpy
data = numpy.asarray([1,2,3,4,5])
dists = data.reshape((1,5)) / data.reshape((5,1))
print dists
which = dists.argmin()
(r,c) = (which // 5, which % 5) # assumes C ordering
# pick whichever is most appropriate for you...
minval = dists[r,c]
minval = dists.min()
minval = dists.ravel()[which]
Source: Stackoverflow.com