calculate daily mean of an array in python

Question

I want to calculate the daily mean of an array of values without considering negative values.

I use this array of data:

Val=['45','25','45','26','-999','87','9','5','4','5','78','98','14','25',
     '34','15','15','14'...]

that represents the hourly values of one month (30 days).

I tried to remove the negative values from the average but I didn't succeed.

What is the simplest way, in python, to calculate the daily mean and to get an array of 30 values?

Thanks for your help

Here is the code:

f=open('file.csv')

csv_f=csv.reader(f)

val=[]

for row in csv_f:

   val.append(row[0])

for i in range(0,len(val[:])-24,24):

   j=i+24

   mean(val[i:j])

are the values stored as strings?

Dimitris Fasarakis Hilliard
– Dimitris Fasarakis Hilliard

2015-09-05 13:56:32 +00:00
Commented Sep 5, 2015 at 13:56 — Dimitris Fasarakis Hilliard
– Dimitris Fasarakis Hilliard, Commented Sep 5, 2015 at 13:56
How did you attempt to do it?

martineau
– martineau

2015-09-05 14:14:28 +00:00
Commented Sep 5, 2015 at 14:14 — martineau
– martineau, Commented Sep 5, 2015 at 14:14

Akavall · Accepted Answer · 2015-09-05 14:03:38Z

1

Here is one option:

Say you have array of 6 values and your interested in means on non-negative values of 3 element blocks (24 element blocks in your case).

In [14]: a = np.array([3,4,-999,5,-100,6], dtype=np.float)

In [15]: a[a < 0] = np.nan

In [16]: np.nanmean(a.reshape((-1, 3)), axis=1)
Out[16]: array([ 3.5,  5.5])

answered Sep 5, 2015 at 14:03

Akavall

86.8k58 gold badges214 silver badges261 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user5276228 Over a year ago

Thanks, but what the a.reshape((-1,3)),axis=1) means ? When I try it, i get this error : np.nanmean(a.reshape((-1,24)),axis=1) ValueError: total size of new array must be unchanged

Akavall Over a year ago

@user5276228, a.reshape(-1, 3) means that your are reshaping an 1D array, into a 2D array with 3 columns and however many rows. ValueError: total size of new array must be unchanged means that total number of elements in your array is not divisible by 24.

Brendan Doherty · Accepted Answer · 2015-09-05 17:00:27Z

1

try list comprehension with an IF condition together with int(). Need to slice original value list into daily chunks first

import random

values = random.sample(range(-5, 100), 96)

def mean(l):
    # list comprehension with if condition to remove negatives and cast to int
    l = [int(numeric_string) for numeric_string in l if int(numeric_string) > 0]

    return sum(l) / len(l)

def chunk(l, n):
    # slice the values list into n sized chunks
    return [l[int(i):int(i) + n] for i in range(0, len(l), n)]

y = [ mean(day) for day in chunk(values, 24)]

print(y)

edited Sep 5, 2015 at 17:00

answered Sep 5, 2015 at 14:11

Brendan Doherty

1482 silver badges6 bronze badges

1 Comment

user5276228 Over a year ago

But where do I mention that I want the daily average (each 24 element blocks) ?

serge-sans-paille · Accepted Answer · 2015-09-05 14:05:22Z

0

Assuming Val contains strings, 24 values per day (so len(Val) is a multiple of 24):

# turn the 1D input array into a 2D array, one line per day
DailyVals = [[int(h) for h in Val[i:i+24]]
             for i in range(len(Val)/24)]
# prune negative values
ValidVals = [[h for h in day if h >= 0]
             for day in DailyVals]
# compute the mean
Mean = [sum(val) / len(val) for val in ValidVals]

answered Sep 5, 2015 at 14:05

serge-sans-paille

2,13913 silver badges10 bronze badges

Comments

martineau · Accepted Answer · 2015-09-05 14:27:59Z

0

Something like this would avoid having to create temporary lists:

vals = ['45','25','45','26','-999','87','9',
        '5','4','5','78','98','14','25',
        '34','15','15','14']

daily_mean = (sum(int(v) for v in vals if int(v) > -1) /
              sum(1 for v in vals if int(v) > -1)

answered Sep 5, 2015 at 14:27

martineau

124k29 gold badges181 silver badges319 bronze badges

Collectives™ on Stack Overflow

calculate daily mean of an array in python

4 Answers 4

2 Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related