Question

在（3987）和（5026）范围内的字段[Num]中的数字的平均值是多少？

该字段位于excel下方的字段[4]。

**amount       code    quan val     number  Random**
2.11    I[N8U7]:75  184 Blue    2254    Potato
3.13    Z[V0L8]:64  131 Blue    6349    Carrot
4.24    B[Y1U2]:38  56  Blue    4164    Mushrooms
7.32    T[Z7N0]:67  329 Red     2079    Pear
9.1     C[T8C5]:83  344 Blue    1045    Apple
11.17   M[P4J9]:38  267 Blue    1254    Strawberry
2.21    E[S1G7]:62  446 Red     2223    Vanilla
1.41    W[M4M5]:96  8   Red     6745    Juice
2.31    W[P3E1]:24  215 Red     1223    Orange
0.12    E[M5K0]:78  424 Blue    2385    Pineapple
3.91    A[A9M2]:33  367 Red     3354    Grape
3.1     W[N2E2]:70  121 Blue    7716    Watermelon
10.21   J[H2W8]:17  253 Red     1017    Yogurt
5.1     G[K5L5]:08  216 Red     1039    Peppers
1.14    V[Z2C3]:L75 419 Blue    2520    Onions
1.02    Q[I1I2]:20  380 Red     2700    Chocolate
0.19    S[P1X2]:43  133 Blue    3171    Cheese
7.21    Z[B2E3]:46  126 Blue    2971    Ham
10.21   L[F6V1J:28  249 Red     7574    Blueberry
1.02    X[B0N3]:65  243 Blue    3441    Water

我尝试了以下代码，但我无法弄清楚还有什么要做。提前致谢

file=open ('3114644b.csv','r')

def mylist():
    alist=[]
    for line in file:
        field = line.split(',')
        if field[0]=='bid' or field[0]=='leave':
            alist.append(float(field[4]))
    return alist

blist=mylist()
total = 0
count = 0
for num in blist:
    total +=  num
    count += 1

average = total / count

print ("the average of the values)

file.close

Answer 1

使用csv module，它专为此类任务而设计：

import csv

total = count = 0

with open('3114644b.csv', newline='') as f:
    reader = csv.reader(f)
    next(reader, None)  # skip the first row of headers

    for row in reader:
        total += float(row[4])
        count += 1

if count:
    # only calculate the average if there was actually anything in the file
    average = total / count
    print('The average of the values is {}'.format(average))

上面的代码也使用该文件作为上下文管理器（带有with语句）;只要with块完成，文件就会自动关闭。

在您的版本中，您尝试手动关闭文件，但只设法引用.close()方法，而不是实际调用它。

我们也不会将所有值都读入列表，而不是只能对值进行求和并计算总和值的数量。这样可以节省更少的内存，并且可以快速高效地处理巨大的CSV文件。

对于您的样本数据，上面的代码输出：

值的平均值为3261.2

Answer 2

这是一个不使用cvs模块的版本。（请注意，鼓励您学习如何使用合适的模块（如果每个任务都存在）

data = []

# This next line closes the file as soon as the block ends (as Martijn suggests)
with open ('3114644b.csv','r') as f:
    for line in f:
        field = line.split(',')
        if field[0] in {'bid', 'leave'}:
            # Note that the 4th column you want to refer to is actually the list
            # list elemnt with index 3, not 4. List indexes start with 0
            data.append(float(field[3]))

# The 'sum()' function is the best choice for your problem as karthirk suggested
# The 'len()' function is a built-in function that returns the number of items
# a list has
average = sum(data)/len(data)

print ("The average of the values is %f" % average)

在Python上查找平均值

2 个答案: