百度地图API绘制出租车流向地图（一）：将起始GPS点映射到地图上
打算在年前实现用百度地图API绘制NYC出租车流向地图。目前实现了将出租车的起始点的GPS点映射到地图上，绘制了GPS点的热力图。记录在此。
所用数据：NYC绿色出租车数据
时间：2016.01.01 0:00-24:00 共24小时
GPS点个数：64398
绘图方式：热力图
百度地图API提供自定义热力图（Heatmap）功能，网站上提供示例代码。
将经纬度数据喂进去即可。
记录一下csv文件转json文件：
绿色出租车csv数据包括上下车时间、上下车的经纬度，载客人数、各种收费计算，只读其中的上车点经纬度数据。
1.使用reader函数，返回一个生成器，类型为列表：
import csv
with open('example.csv','rb') as csvfile:
reader = csv.reader(csvfile)
rows= [row for row in reader]
- 读取其中的一列：
import csv
with open('A.csv','rb') as csvfile:
reader = csv.reader(csvfile)
column = [row[2] for row in reader]
#读其中的第3列
- 读取其中的一行：
下面代码打印出row[2]代表的值，也就是第三行
with open(csv_file, "r") as f:
reader = csv.reader(f)
row1 = [row for row in reader]
print row1[2] #row1[i]就代表是第几行
- 读取指定的某行某列
如果想打印出第一列第一行的值，直接
print column1[0]
2.使用DictReader
从csv读出的都是str类型。这种方法要事先知道列的序号，比如longitude在第5列，而不能根据’longtitude’这个标题查询。这时可以采用DictRead函数
如果我们想用DictReader读取csv的某一列，就可以用列的标题查询：
#直接用列标题 Pickup_longitude 来读
with open(file1,"r") as csvfile1:
reader = csv.DictReader(csvfile1)
Pickup_longitude = [row['Pickup_longitude'] for row in reader]
3. 将读取的某几列写入到新的csv文件：
with open(file2,"w") as csvfile2:
print(len(Pickup_longitude), len(Pickup_latitude))
writer = csv.writer(csvfile2)
writer.writerow(['lng','lat','count'])
#for index in range(len(Pickup_latitude)):
for index in range(num):
writer.writerow([float(Pickup_longitude[index]),float(Pickup_latitude[index]),float(1)])
将处理好的csv文件转json文件
def read_csv(file):
csv_rows = []
with open(file) as csvfile:
reader = csv.DictReader(csvfile)
title = reader.fieldnames
for row in reader:
csv_rows.extend([{title[i]:float(row[title[i]]) for i in range(len(title))}])
return csv_rows
# 写json文件
def write_json(data, json_file, format=None):
with open(json_file, "w") as f:
if format == "good":
f.write(json.dumps(data, sort_keys=False, indent=4, separators=(',', ': '),encoding="utf-8",ensure_ascii=False))
else:
f.write(json.dumps(data))
write_json(read_csv('G:/nyc/data.csv'), 'data.json')
附完整代码：
import csv
import json
def csv2csv(file1,file2):
Pickup_longitude = []
Pickup_latitude = []
with open(file1,"r") as csvfile1:
reader = csv.DictReader(csvfile1)
Pickup_longitude = [row['Pickup_longitude'] for row in reader]
# Pickup_latitude = [row2['Pickup_latitude'] for row2 in reader]
with open(file1, "r") as csvfile1:
reader = csv.DictReader(csvfile1)
Pickup_latitude = [row['Pickup_latitude'] for row in reader]
with open(file2,"w") as csvfile2:
print(len(Pickup_longitude), len(Pickup_latitude))
writer = csv.writer(csvfile2)
writer.writerow(['lng','lat','count'])
for index in range(len(Pickup_latitude)): writer.writerow([float(Pickup_longitude[index]),float(Pickup_latitude[index]),float(1)])
csv2csv('G:/nyc/green_tripdata_2016-01.csv','G:/nyc/data.csv')
def read_csv(file):
csv_rows = []
with open(file) as csvfile:
reader = csv.DictReader(csvfile)
title = reader.fieldnames
for row in reader:
csv_rows.extend([{title[i]:float(row[title[i]]) for i in range(len(title))}])
return csv_rows
# 写json文件
def write_json(data, json_file, format=None):
with open(json_file, "w") as f:
if format == "good":
f.write(json.dumps(data, sort_keys=False, indent=4, separators=(',', ': '),encoding="utf-8",ensure_ascii=False))
else:
f.write(json.dumps(data))
write_json(read_csv('G:/nyc/data.csv'), 'data.json')