How do I find the median of a list in python

Question

I am trying to find the median of a list. I have tried it two ways and it hasn't worked in either (I have imported what I need and the list is there) selfies is the name of the list

def median():
    return numpy.median(numpy.array(selfies))

this is the error

ret = umr_sum(arr, axis, dtype, out, keepdims)

TypeError: cannot perform reduce with flexible type

and the other way was

def median():
    med = statistics.median(selfies)
    return med

the error is

return (data[i - 1] + data[i])/2

TypeError: unsupported operand type(s) for /: 'str' and 'int'

Thank you in advance

Possible duplicate of [Finding median of list in Python](https://stackoverflow.com/questions/24101524/finding-median-of-list-in-python) — Vinícius Figueiredo, Jul 10 '17 at 04:31
That's what I want to confirm, it seems to me by error messages. — eyllanesc, Jul 10 '17 at 04:35
To ask a good question you should read: https://stackoverflow.com/help/how-to-ask — eyllanesc, Jul 10 '17 at 04:36
You can display the contents of the list, are they integers, floating, strings? — eyllanesc, Jul 10 '17 at 04:56

Er CEO Vora Mayur · Accepted Answer · 2017-07-10T09:07:15.643

Hello User9123,

Main Use of the Medain() function

This module provides functions for calculating mathematical statistics of numeric (Real-valued) data.

Note Unless explicitly noted otherwise, these functions support int, float, decimal.Decimal and fractions.Fraction. Behaviour with other types (whether in the numeric tower or not) is currently unsupported. Mixed types are also undefined and implementation-dependent. If your input data consists of mixed types, you may be able to use map() to ensure a consistent result, e.g. map(float, input_data).

Your Problem

When you use this function for the string so it is not work properly some time so better i suggest you used custom function. I give the solution in my below code.

Explanation Function Median()

statistics.median(data)

Return the median (middle value) of numeric data, using the common “mean of middle two” method. If data is empty, StatisticsError is raised. data can be a sequence or iterator.

The median is a robust measure of central location, and is less affected by the presence of outliers in your data. When the number of data points is odd, the middle data point is returned:

Solution of Problem

If you use this function for the numeric value so try this below code,

def getMedian(numericValues):
  theValues = sorted(numericValues)

  if len(theValues) % 2 == 1:
    return theValues[(len(theValues)+1)/2-1]
  else:
    lower = theValues[len(theValues)/2-1]
    upper = theValues[len(theValues)/2]
    return (float(lower + upper)) / 2 


print getMedian([0,1,2,3,4,5]) # output = 2.5

If you are use median function for the string so try this below code,

def medianFind(mystring):
    return mystring[(len(mystring)-1)/2]  #len returns the length of the string

print medianFind("vmr")  #prints m

I hope my answer is helpful.
If any query so comment please.

The error messages are not by the calculation of the median itself, but by the data type. Your answer does not answer the OP. — eyllanesc, Jul 10 '17 at 05:06
Hello mr. eyllanesc irst you show my answer i give solution using another. — Er CEO Vora Mayur, Jul 10 '17 at 05:18
you are expert so give first comment after not update my anwer so give downvote. — Er CEO Vora Mayur, Jul 10 '17 at 05:18
If the question was like finding the median of a list of floating or integers (numerical elements) your answer would be correct, but it is not, you could consult the author and ask for information. — eyllanesc, Jul 10 '17 at 05:21

score -1 · Answer 2 · answered Jul 10 '17 at 04:44

-1

Use a .sort() or .sorted() to sort your list according to how you want, then retrieve list[math.floor(len(list)/2)].

If you don't need to sort it and just want the middle value, use

list[math.floor(len(list)/2)].

answered Jul 10 '17 at 04:44

Julian Chan

450
2
8

The error messages are not by the calculation of the median itself, but by the data type. Your answer does not answer the OP – eyllanesc Jul 10 '17 at 05:06
@eyllanesc But using .sort() he can then use his own comparison method for sorting (which seems easier than declaring __cmp__ or __eq__, especially if the object is imported in from external libraries), so wouldn't this solve his problem? Ultimately, I am under the impression that he is looking for the median, and his issues lie with the numpy library and the data type he is using, but since median is not overly complex, I am just suggesting he does it manually, since using my method would probably resolve TypeError. – Julian Chan Jul 10 '17 at 05:32
Your solution answers the question if the list were strings? For example `l = ['1', '2', '3', '4']` – eyllanesc Jul 10 '17 at 05:34
@eyllanesc Yes it does: l.sorted(l,key = lambda x: int(x)) then get the median (assuming int() doesn't throw an error and all the strings can be converted to int). You could also use other comparison "standards" like ASCII or anything in the world you could think of as long as it allows for valid comparison. It can also handle other data types as well. – Julian Chan Jul 10 '17 at 05:43

How do I find the median of a list in python

2 Answers2

Main Use of the Medain() function

Your Problem

Explanation Function Median()

Solution of Problem