Flightradar24 pandas groupby 和矢量化。无循环解决方案

Question

我希望对飞行雷达数据执行快速操作，以查看距离上的速度是否与报告的速度相匹配。我有多个航班，并被告知不要在 pandas 数据帧上运行双循环。这是一个示例数据框：

import pandas as pd
from datetime import datetime
from shapely.geometry import Point
from geopy.distance import distance

dates = ['2020-12-26 15:13:01', '2020-12-26 15:13:07','2020-12-26 15:13:19','2020-12-26 15:13:32','2020-12-26 15:13:38']
datetimes = [datetime.fromisoformat(date) for date in dates]
data = {'UTC': datetimes, 
        'Callsign': ["1", "1","2","2","2"],
        'Position':[Point(30.542175,-91.13999200000001), Point(30.546204,-91.14020499999999),Point(30.551443,-91.14417299999999),Point(30.553909,-91.15136699999999),Point(30.554489,-91.155075)]
       }
df = pd.DataFrame(data)

我想做的是添加一个名为“dist”的新列。如果它是新呼号的第一个元素，则此列将为 0，否则将为点与前一个点之间的距离。

生成的 df 应如下所示：

df1 = df
dist = [0,0.27783309075379214,0,0.46131362750613436,0.22464461718704595]
df1['dist'] = dist

我尝试的是首先分配一个组索引：

df['group_index'] = df.groupby('Callsign').cumcount()

然后分组

然后尝试应用函数：

df['dist'] = df.groupby('Callsign').apply(lambda g: 0 if g.group_index == 0 else distance((g.Position.x , g.Position.y),
    (g.Position.shift().x , g.Position.shift().y)).miles)

我希望这会给我每个组的第一个索引为 0，然后在所有其他组上运行距离函数并返回一个以英里为单位的值。但是它不起作用。

代码出错的原因至少有一个，因为在系列而不是对象上调用了 shapely 对象的 .x 和 .y 属性。

任何关于如何解决此问题的想法将不胜感激。

Answer 1

1. 按呼号然后时间戳排序df
2. 使用移位点的临时列计算相邻行之间的距离
3. 对于每个新呼号的第一行，将距离设置为 0
4. 删除临时列

df = df.sort_values(by=['Callsign', 'UTC'])

df['Position_prev'] = df['Position'].shift().bfill()

def get_dist(row):
return distance((row['Position'].x, row['Position'].y),
                (row['Position_prev'].x, row['Position_prev'].y)).miles

df['dist'] = df.apply(get_distances, axis=1)

# Flag row if callsign is different from previous row callsign
new_callsign_rows = df['Callsign'] != df['Callsign'].shift()

# Zero out the first distance of each callsign group
df.loc[new_callsign_rows, 'dist'] = 0.0

# Drop shifted column
df = df.drop(columns='Position_prev')

print(df)

                  UTC Callsign                              Position      dist
0 2020-12-26 15:13:01        1  POINT (30.542175 -91.13999200000001)  0.000000
1 2020-12-26 15:13:07        1  POINT (30.546204 -91.14020499999999)  0.277833
2 2020-12-26 15:13:19        2  POINT (30.551443 -91.14417299999999)  0.000000
3 2020-12-26 15:13:32        2  POINT (30.553909 -91.15136699999999)  0.461314
4 2020-12-26 15:13:38        2          POINT (30.554489 -91.155075)  0.224645