Pandas 手动计算平均值或标准差

Question

Apart from the min and max value, we also want the mean and variance of the Kilometers_Driven in different location. Using the iterative method, do the following:

Find all of the unique location in the dataset.

Start the timer.

For a unique location, iterate through the dataset once to calculate the mean of the Kilometers_Driven.

For the same unique location, iterate through the dataset once more to calculate the variance of the Kilometers_Driven.

8.5 Repeat for all of the unique locations. Iteratively, calculate the mean and variance of the Kilometers_Driven for different location. Measure the time it takes.

Stop the timer. Print out the mean and variance of the Kilometers_Driven for each location as well as the time elapsed.

My codes are below:

#8.1
df.Location.unique()

#8.2
start = timeit.default_timer()

#8.3 Calculating mean of "Kilometers_Driven" manually (For a unique location?)
col_mean = 0.0
for row in range(len(df)):
    col_mean += df.loc[row, "Kilometers_Driven"]
col_mean /= len(df)
print(col_mean)

#8.4 Calculating variance of "Kilometers_Driven" manually
col_var = 0.0
for row in range(len(df)):
    col_var += (df.loc[row, "Kilometers_Driven"] - col_mean)**2
col_var /= len(df) - 1 
print(col_var)

#8.5 How to do?

#8.6 Setting Stop Time
stop = timeit.default_timer()

t_custom = stop - start

print(f"Time elapsed {t_custom} s")

it works but For a unique location, iterate through the dataset once to calculate the mean of the Kilometers_Driven. in 8.3. I just Calculating mean of "Kilometers_Driven" manually.I am not sure how to correct it. And not sure how to do question in 8.5. Anyone can help me? Thanks in advance!!

Answer 1

for l in list(df.Location.unique()): 
    col_mean = 0.0

    num_rows=0
    for row in range(len(df)):
        if df.loc[row, 'Location'] == l:
              num_rows += 1
              col_mean += df.loc[row, "Kilometers_Driven"]
    col_mean = col_mean/num_rows

    print( 'Location: %s mean %.2f' % (l, col_mean) )