pandas.core.common.PandasError：未正確調用DataFrame構造函數

Question

我正在嘗試使用mosquitto接收數據，並使用python pandas將其另存為csv文件。 數據是連續的，直到我停止腳本為止。

mqtt_pub.py

import paho.mqtt.client as mqtt
import random
import schedule
import time

mqttc = mqtt.Client("python_pub")
mqttc.connect("localhost", 1883)

def job():
    mqttc.publish("hello/world", random.randint(1, 10))

schedule.every(1).seconds.do(job)

while True:
    schedule.run_pending()
    time.sleep(1)

mqttc.loop(2)

mqtt_sub.py

import paho.mqtt.client as mqtt
import pandas as pd

def on_connect(client, userdata, rc):
    print("Connected with result code "+str(rc))
    client.subscribe("hello/world")

def on_message(client, userdata, msg):
    datas = map(int, msg.payload)
    for num in datas:
        df = pd.DataFrame(data=datas, columns=['the_number'])
        df.to_csv("testing.csv")

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("localhost", 1883, 60)

client.loop_forever()

從上面mqtt_sub.py腳本，我得到testing.csv ，看起來像這樣

    | the _number
0   | 2

2是我停止mqtt_sub.py腳本之前收到的最后一位數字

Connected with result code 0
[3]
[9]
[5]
[3]
[7]
[2]
...
...
KeyboardInterrupt

我希望得到這樣的testing.csv

    | the_number
0   | 3
1   | 9
2   | 5
...
...
5   | 2

為此，我嘗試將以下df = pd.DataFrame(data=datas, columns=['the_number'])更改為df = pd.DataFrame(data=num, columns=['the_number'])和以下錯誤發生

pandas.core.common.PandasError: DataFrame constructor not properly called!

有人知道如何解決錯誤嗎？ 我也覺得我在這里沒有正確使用for循環。

感謝您的建議和幫助。

[UPDATE]

我在on_message方法中添加/更改以下行

def on_message(client, userdata, msg):
    datas = map(int, msg.payload)
    df = pd.DataFrame(data=datas, columns=['the_number'])

    f = open("test.csv", 'a')
    df.to_csv(f)
    f.close()

在Nulljack的幫助下，我可以在CSV文件中獲得像這樣的結果

   | the_number
0  | 3
   | the_number
0  | 9 
   | the_number
0  | 5
   | the_number
0  | 3
   | the_number
0  | 7

我的目標是在CSV文件中實現類似的目標

   | the_number
0  | 3
1  | 9
2  | 5 
3  | 3
4  | 7

Answer 1

如果我的理解是錯誤的，在向我道歉之前從未使用過蚊子。

在我看來，每次mqtt_pub.py發布消息（例如，每隔一秒鍾）時，都會運行mqtt_sub.py中的on_message方法，這將導致您每次發布消息時覆蓋您的testing.csv文件

為了解決這個問題，我會在您的on_connect方法中初始化一個數據框，然后在on_message中通過df.append將新值添加到該數據框

至於終止后寫到csv，我不確定。

希望這可以幫助

Answer 2

其他線程很擁擠，所以我在這里移動了我的回復

嘗試使用以下代碼

import paho.mqtt.client as mqtt
import pandas as pd

# Move df here 
df = pd.DataFrame(columns=['the_number'])

def on_connect(client, userdata, rc):
    print("Connected with result code "+str(rc))
    client.subscribe("hello/world")

def on_message(client, userdata, msg):
    datas = map(int, msg.payload)

    # this adds the data to the dataframe at the correct index
    df.iloc[df.size] = datas

    # I reverted this line back to what you originally had 
    # This will overwrite the testing.csv file every time your subscriber
    # receives a message, but since the dataframe is formatted like you want 
    # it shouldn't matter 
    df.to_csv("testing.csv")


client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("localhost", 1883, 60)

client.loop_forever()