如何在for循環中為Pandas DataFrame的特定行設置值？

Question

for petid in X['PetID']:
    sentiment_file = datapath + '/train_sentiment/' + petid + '.json'
    if os.path.isfile(sentiment_file):
        json_data = json.loads(open(sentiment_file).read())
        X['DescriptionLanguage'] = json_data['language']
        X['DescriptionMagnitude'] = json_data['documentSentiment']['magnitude']
        X['DescriptionScore'] = json_data['documentSentiment']['score']
        # print(petid, sentiment_file,
        #       json_data['documentSentiment']['magnitude'])
    else:
        X['DescriptionLanguage'] = 'Unknown'
        X['DescriptionMagnitude'] = 0
        X['DescriptionScore'] = 0

這就是我所擁有的，但這不起作用。 它將每行設置為具有DescriptionLanguage ， DescriptionMagnitude和DescriptionScore 。

Answer 1

您可以使用.loc設置單個值，而不是整個列。 這是一個包含的示例

import pandas as pd
import numpy as np

X = pd.DataFrame(np.arange(5), columns=['PetID'])

for ind, row in X.iterrows():
    petid = row['PetID']
    X.loc[ind, 'DescriptionLanguage'] = 'No description for {}'.format(petid)

Answer 2

除了@Heikki Pulkkinen的出色答案之外，您還可以為數據框中的各個列建立索引，例如：

import pandas as pd
import numpy as np
data = np.array([np.arange(10)]*4).T
X = pd.DataFrame(data,columns=["PetID","DescriptionLanguage","DescriptionMagnitude","DescriptionScore"])
for i in range(len(X['PetID'])):
    X['DescriptionLanguage'][i] = 10*i

...導致X變成：

    PetID   DescriptionLanguage DescriptionMagnitude    DescriptionScore
0   0       0                   0                       0
1   1       10                  1                       1
2   2       20                  2                       2
3   3       30                  3                       3
4   4       40                  4                       4
5   5       50                  5                       5
6   6       60                  6                       6
7   7       70                  7                       7
8   8       80                  8                       8
9   9       90                  9                       9