计算python中特定列的数字出现次数

Question

I am trying to do the equivalent of a COUNTIF() function in excel. I am stuck at how to tell the .count() function to read from a specific column in excel.

I have

df = pd.read_csv('testdata.csv')    
df.count('1') 

but this does not work, and even if it did it is not specific enough. I am thinking I may have to use read_csv to read specific columns individually.

Example:

Column name
4
4
3
2
4
1

the function would output that there is one '1' and I could run it again and find out that there are three '4' answers. etc.

I got it to work! Thank you

I used:

print (df.col.value_counts().loc['x']

Answer 1

If all else fails, why not try something like this?

import numpy as np
import pandas
import matplotlib.pyplot as plt

df = pandas.DataFrame(data=np.random.randint(0, 100, size=100), columns=["col1"])

counters = {}
for i in range(len(df)):
    if df.iloc[i]["col1"] in counters:
        counters[df.iloc[i]["col1"]] += 1
    else:
        counters[df.iloc[i]["col1"]] = 1

print(counters)
plt.bar(counters.keys(), counters.values())
plt.show()

Answer 2

Here is an example of a simple 'countif' recipe you could try:

import pandas as pd

def countif(rng, criteria):
    return rng.eq(criteria).sum()

Example use

df = pd.DataFrame({'column1': [4,4,3,2,4,1],
                   'column2': [1,2,3,4,5,6]})
countif(df['column1'], 1)