Tuple pairs, finding minimum using python

Question

I want to find the minimum of a list of tuples sorting by a given column. I have some data arranged as a list of 2-tuples for example.

data = [ (1, 7.57), (2, 2.1), (3, 1.2), (4, 2.1), (5, 0.01),           (6, 0.5), (7, 0.2), (8, 0.6)] 

How may I find the min of the dataset by the comparison of the second number in the tuples only?

i.e.

data[0][1] = 7.57 data[1][1] = 2.1 

min( data ) = (5, 0.01)

min( data ) returns (1, 7.57), which I accept is correct for the minimum of index 0, but I want minimum of index 1.

Answer 1

In [2]: min(data, key = lambda t: t[1]) Out[2]: (5, 0.01) 

or:

In [3]: import operator  In [4]: min(data, key=operator.itemgetter(1)) Out[4]: (5, 0.01) 

Answer 2

Using numpy, you can use these commands to get the tuple in list where item is minimum:

The ingredients that make this work are numpy's advanced array slicing and argsort features.

import numpy as np #create a python list of tuples and convert it to a numpy ndarray of floats data = np.array([ (1, 7.57), (2, 2.1), (3, 1.2),                    (4, 2.1), (5, 0.01), (6, 0.5), (7, 0.2), (8, 0.6)])  print("data is") print(data)  #Generate sortIndices from second column sortIndices = np.argsort(data[:,1])  print("sortIndices using index 1 is:" ) print(sortIndices) print("The column at index 1 is:") print(data[:,1]) print("Index 1 put into order using column 1") print(data[sortIndices,1]) print("The tuples put into order using column 1") print(data[sortIndices,:]) print("The tuple with minimum value at index 1") print(data[sortIndices[0],:]) print("The tuple with maximum value at index 1") print(data[sortIndices[-1],:]) 

Which prints:

data is [[ 1.    7.57]  [ 2.    2.1 ]  [ 3.    1.2 ]  [ 4.    2.1 ]  [ 5.    0.01]  [ 6.    0.5 ]  [ 7.    0.2 ]  [ 8.    0.6 ]]  sortIndices using index 1 is: [4 6 5 7 2 1 3 0]  The column at index 1 is: [ 7.57  2.1   1.2   2.1   0.01  0.5   0.2   0.6 ]  Index 1 put into order using column 1 [ 0.01  0.2   0.5   0.6   1.2   2.1   2.1   7.57]  The tuples put into order using column 1 [[ 5.    0.01]  [ 7.    0.2 ]  [ 6.    0.5 ]  [ 8.    0.6 ]  [ 3.    1.2 ]  [ 2.    2.1 ]  [ 4.    2.1 ]  [ 1.    7.57]]  The tuple with minimum value at index 1 [ 5.    0.01]  The tuple with maximum value at index 1 [ 1.    7.57]