从csv文件获取最大值和最小值，其中(case)

Question

我有以下csv文件，其中包含以下行：

;name;;;surname;;age;salary;
0;john;;;snow;;38;1000;
1;nick;;;kalathes;;22;500;
0;roger;;;smith;;21;400;
1;mona;;;liza;;18;1000;
1;bill;;;alios;;48;2000;

我使用csv.reader读取csv文件

import csv,sys
filename='test1.csv'
with open(filename, mode='r', newline='', encoding='utf-8') as f:
    reader=csv.reader(f)
    try:
        for row in reader:
            print(row)

输出：

[';name;;;surname;;age;salary;']
['0;john;;;snow;;38;1000;']
['1;nick;;;kalathes;;22;500;']
['0;roger;;;smith;;21;400;']
['1;mona;;;liza;;18;1000;']
['1;bill;;;alios;;48;2000;']

我的目标是找出行以"1"开头时的最大年龄。我想作为第一步，我必须找出字符串'age'在第一行的位置。(在本例中，年龄是第七个元素(用;分隔)。

我通过尝试这样的方式来解决这个问题：

for row in reader:
    print(row)
    print(type(row))
    indexes = [i for i,x in enumerate(row) if x == "age"]
    print(indexes)

但到目前为止还没有成功。我认为，当我能够知道它的位置时，我将必须检查是否有任何行以"1"开头。在那之后，我必须从这些行中找到最大值和最小值。我可以用java，javscript，c等来写，但是我对python还是个初学者。我必须实现的伪代码可能是这样的：

for(i=0; i<list.length; i++ {
    if (list.includes("age") {
        position=stringAt(age)
        break;
    }
for(i=0; i<list.length; i++ {
   if (list[0]==1) {
       tmp.push(list[position]
}
print(max.tmp)

Answer 1

指定分号作为分隔符，这样就很简单了：

reader = csv.reader(f, delimiter=';')
ages = [row[6] for row in reader if row[0] == '1']
max_age = sorted(ages)[-1]

Answer 2

我会使用DictReader以及内置的min和max函数：

import csv,sys
filename='test1.csv'
with open(filename, mode='r', newline='', encoding='utf-8') as f:
    reader=csv.DictReader(f, delimiter=";")
    print(min(int(row['age']) for row in reader))
with open(filename, mode='r', newline='', encoding='utf-8') as f:
    reader=csv.DictReader(f, delimiter=";")
    print(max(int(row['age']) for row in reader))

如果数据得不到保证，您可能需要使用try和except。

Answer 3

由于您的CSV文件由分号分隔，因此您需要在创建csv.reader时指定分号。其余的处理过程相对简单：

import csv, sys

DELIMITER = ';'
FILENAME = 'minmax_test.csv'

with open(FILENAME, mode='r', newline='', encoding='utf-8') as f:
    reader = csv.reader(f, delimiter=DELIMITER)

    # Find index of "age" field.
    header = next(reader)
    for i, field in enumerate(header):
        if field == 'age':
            age_index = i
            break
    else:
        raise RuntimeError('No field named "age" found in csv file')

    # Find min and max ages of rows that start with "1".
    min_age, max_age = sys.maxsize, -sys.maxsize-1
    min_age_row, max_age_row = None, None
    min_age_name, max_age_name = '', ''

    for i, row in enumerate(reader):
        print('row[{}]: {}'.format(i, row))
        if row[0] == '1':
            age = int(row[age_index])
            if age < min_age:
                min_age = age
                min_age_row = i
                min_age_name = row[1]
            if age > max_age:
                max_age = age
                max_age_row = i
                max_age_name = row[1]

    print('min - name: {!r}, age: {} in row {}'.format(min_age_name, min_age, min_age_row))
    print('max - name: {!r}, age: {} in row {}'.format(max_age_name, max_age, max_age_row))

输出：

row[0]: ['0', 'john', '', '', 'snow', '', '38', '1000', '']
row[1]: ['1', 'nick', '', '', 'kalathes', '', '22', '500', '']
row[2]: ['0', 'roger', '', '', 'smith', '', '21', '400', '']
row[3]: ['1', 'mona', '', '', 'liza', '', '18', '1000', '']
row[4]: ['1', 'bill', '', '', 'alios', '', '48', '2000', '']
min - name: 'mona', age: 18 in row 3
max - name: 'bill', age: 48 in row 4