CODEWITHSUNDEEP
pythonlistcsvmaxmin
Nakos Kotsanis
Nakos Kotsanis

Reputation: 300

Get maximum and minimum from csv file where (case)

I have the following csv file which contains these rows:

;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;

I read csv file using csv.reader:

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)

Output:

[';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;']

My goal is to find the maximum age if a row starts with "1". I suppose that as a first step I have to find out the position of string 'age' at the first row. (in this example age is the seventh element (separated by ;).

I work on that by trying something like:

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

But had no success so far. I think that when I will be able to know the position of that I will have to check if any rows start with "1". after that I have to find the max and the min from these rows. I'm able to do it in java, javscript, c, etc. but I'm a beginner in python. A pseudo-code I have to implement may be something like:

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)

Upvotes: 0

Views: 1329

Answers (4)

Mark Bailey
Mark Bailey

Reputation: 1675

I'd use DictReader and the min and max built in functions:

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))

You may need to use try and except if the data is not guaranteed.

Upvotes: 2

martineau
martineau

Reputation: 123521

Since your CSV file is delimited by semicolons, you need to specify that when creating the csv.reader. The rest of the processing is relatively straight-forward:

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))

Output:

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

Upvotes: 2

Colin
Colin

Reputation: 10820

Specify semicolon as your delimiter, then it's fairly straightforward:

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

Upvotes: 2

exiz
exiz

Reputation: 93

You should always read the docs (CSV File Reading and Writing).

Your CSV is not a "standard" CSV file so you need to specify your delimiter (';')

reader=csv.reader(f, delimiter=';')

Now your output will be as follow:

['0','john','','','snow','','38','1000','']

['1','nick','','','kalathes','','22','500','']

Upvotes: 1

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