Python中缺少的数据

Question

我正在尝试将一个JSON文件导入Python以进行一些数据分析。每个JSON对象都有许多不同的变量(大约7-10)。有些对象有某些变量，而另一些对象则没有。我对每行json中的五个变量特别感兴趣。但是，有些对象缺少数据。我如何使它，使程序将对每一个缺失的数据置入一个零？

import json
data = []
keys = ["hostid","time", "userid","link", "title"]
m = len(keys)

with open('test.json') as json_data:
    for line in json_data:
        dataline = json.loads(line)
        row = []
        for i in xrange(m):
            row.append(dataline[keys[i]])
        data.append(row)
json_data.close()

data = np.array(data)

下面是一些示例JSON对象。如您所见，第一个对象拥有我想要的所有五个变量，但是第二个对象没有"title“变量的数据。

{
"title": "Monster Man", 
"link": "http://monsters4ever.com/tagged/rosemary%27s%20baby%20(1968)",
"userid": 130290, 
"field5": "lezmer Brunch at City Winery? Who Knew? -- Grub Street Chicago\"", 
"hostid": "3969937ab0a3e2db8690c482564006a7", 
"time": 376541
}

{
"link": "http://www.sfgate.com/world/article/WORLD-News-of-the-Day-From-Across-the-Globe-4120318.php", 
"userid": 227954, "field5": "ries « SHEfinds\"", 
"hostid": "6096407936827c96fa0833f26ab33b76", 
"time": 376541
}

有人能帮帮我吗？

Answer 1

我会尝试的。我也只是迭代了一下键列表。

with open('test.json') as json_data:
    for line in json_data:
        dataline = json.loads(line)
        row = []
        for i in keys:#iterate through keys
            try:
                row.append(dataline[i])
            except:
                pass
        data.append(row)
json_data.close()

Answer 2

与其填写丢失的数据，不如尝试从对象检索数据，而不是通常的：x['field']，尝试x.get('field')。

例如：

with open('test.json') as json_data:
    for line in json_data:
        dataline = json.loads(line)
        row = []
        for key in keys:
            row.append(dataline.get(key))

        # better is:
        # row = [dataline.get(key) for key in keys]

        data.append(row)

这是因为如果在字典中找不到键，dict.get会返回None。

如果您真的不想这样做，并且知道您想要的字段，可以使用dict.setdefault将None放在其中：

for field in fields_you_care_about:
    obj.setdefault(field, None)

Answer 3

您可以使用try，因为当您试图调用不存在的键时，它会引发异常：

import json
data = []
keys = ["hostid","time", "userid","link", "title"]
m = len(keys)

with open('test.json') as json_data:
    for line in json_data:
        dataline = json.loads(line)
        row = []
        for i in xrange(m):
            try:
                row.append(dataline[keys[i]])
            except Exception:
                row.append(None)
        data.append(row)
json_data.close()

data = np.array(data)