Finding top 10 max values in for loop Python

Question

I am trying to find the top 10/300 values in a for loop. I understand how to find the max value for the entire loop, but I am trying to calculate 300 values and then only use the top 10 values in those 300.

Here is my for loop:

random.shuffle(folder)
for i in range(len(folder)):
if i < 30:
    phaseresult_i = []
    data = np.loadtxt(dir + folder[i])
    time = data[:,0]-2450000
    magnitude = data[:,1]
    #print ('\n File:', folder[i],'\n','Time:',time,'\n', 'Magnitude:', magnitude)
    t = 10000 * time
    y = np.sin(2 * np.pi * t) * time
    frequency, power = LombScargle(t, y).autopower()
    period = np.log(1/frequency)[np.argmax(power)]
    maxpower = power.max()
    for t in range(len(time)):
        #print(t,time[t])
        floor = math.floor((time[t]-time[0])/period)
        phase_i = ((time[t]-time[0])/period)-floor
        phaseresult_i.append(phase_i)
    maxpower_i.append(maxpower)   
    folder_i.append(folder[i])
else: 
    break

The value I am trying to find the maximums are the top ten max powers and their Periods.

Its hard to understand how your input looks like but this might be helpful.docs.python.org/2/library/… — mad_
– mad_, Commented Oct 1, 2018 at 16:43

jpp · Accepted Answer · 2018-10-02 15:41:29Z

2

You can use heapq.nlargest with a generator to give the top 10 values of an iterable. Here's a trivial example:

from random import sample
from heapq import nlargest

def gen(n):
    yield from sample(range(n), k=n)

res = nlargest(10, gen(100))

[99, 98, 97, 96, 95, 94, 93, 92, 91, 90]

You now only need to convert your logic into a generator function (see 1, 2).

answered Oct 2, 2018 at 15:41

jpp

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vash_the_stampede · Accepted Answer · 2018-10-02 20:04:30Z

1

For demonstration purposes, I shuffled a list of 300 integers, to get the 10 highest values, you would use sorted and then take the range [-10:]

import random

l = [*range(300)]
random.shuffle(l)

print(sorted(l)[-10:])

[290, 291, 292, 293, 294, 295, 296, 297, 298, 299]

Update

random.shuffle(folder)
for i in range(len(folder)):
  max_powers = []
  if i < 3:
    max_powers = []
    phaseresult_i = []
    data = np.loadtxt(dir + folder[i])
    time = data[:,0]-2450000
    magnitude = data[:,1]
    print ('\n File:', folder[i],'\n','Time:',time,'\n', 'Magnitude:', magnitude)
    t = 10000 * time
    y = np.sin(2 * np.pi * t) * time
    # Lomb Scargle Periodogram
    frequency, power = LombScargle(t, y).autopower()
    for period in folder[i]:
        period = np.log(1/frequency)[np.argmax(power)]
        maxpower = power.max()
    max_powers.append((maxpower, i))
    print('\n Max Power = ', maxpower)
    print('\n Period = ', period, '\n ---------------------------')
  print('\n Max Powers, Folder = {}'.format(sorted(max_powers, key=lambda x: x[0])[:-10]))
else:
    break

edited Oct 2, 2018 at 20:04

answered Oct 1, 2018 at 18:05

vash_the_stampede

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12 Comments

hlku2334 Over a year ago

How can I add this into a for loop and get the values for i for the max values.

hlku2334 Over a year ago

For the top ten max powers, I am trying to get the top ten overall from all folders(files) and their associated folder for each max power.

vash_the_stampede Over a year ago

@hluk123 to rephrase dose each iteration of if i <3 have a top ten

vash_the_stampede Over a year ago

print('\n Max Powers, Folder = {}'.format(sorted(max_powers, key=lambda x: x[0])[:-10])) oops forgot this, add the slice in and try, edited this comment fixed parentheses

vash_the_stampede Over a year ago

@hluk123 you could just do for i in sorted(max_powers, key=lambda x: x[0])[:-10] if you just wanted the powers not the file as well you would use i[0] and the i[1] would represent the file if you wanted to isolate either. You could even make a new list , new_list = [i for i in sorted(max_powers, key=lambda x: x[0])[:-10]] again you could isolate using i[0] / i[1] if you dont need the entire tuple

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