数据分析_Pandas中的OLAP(类SQL中窗口函数)
窗口函数: 被称为联机分析函数 (OLAP, Online Anallytical Processing) 或者分析函数(Analytic Function)。
窗口函数允许用户根据数据行与所谓窗口 [so-called window] 中的当前行之间的某种关系对数据行执行计算, 并对每一行数据返回分析结果, 所以使用窗口函数时, 必须始终记住当前行。
+-------------------+| Row |+--- +-------------------+ ---+| +---------------------------------------+ || | +-------------------+ | || | | Row | | || | +-------------------+ | || | +--| Row | | || | | +-------------------+ W| || | Frame| | Current Row | i| || | | +-------------------+ n| |
Function Over| | +--| Row | d| || | +-------------------+ o| || | | Row | w| || | +-------------------+ | || | | Row | | || | +-------------------+ | || | | Row | | || | +-------------------+ | || +---------------------------------------+ |+--- +-------------------+ ---+| Row |+-------------------+
实例数据
使用 Pandas 的 DataFrame 类构建演示数据。
PDF = pd.DataFrame({"deptName":["研发部", "研发部", "产品部", "产品部", "项目部", "项目部", "研发部", "产品部"],"employeeName":["张三", "李四", "王五", "赵六", "李明", "赵亮", "张凯", "赵敏"],"salary":[10000, 13000, 12000, 9000, 12500, 8500, 8900, 12000]}
)print("[Message] Demo Data Based on Pandas DataFrame:")
print(PDF)
输出:
[Message] Demo Data Based on Pandas DataFrame:deptName employeeName salary
0 研发部 张三 10000
1 研发部 李四 13000
2 产品部 王五 12000
3 产品部 赵六 9000
4 项目部 李明 12500
5 项目部 赵亮 8500
6 研发部 张凯 8900
7 产品部 赵敏 12000
Pandas 类窗口聚合函数 (min, max, avg 等)
支持在 Window 上应用所有的标准聚合函数, 如 min, max, avg 等。
SQL 等效语句:
select deptName, employeeName, salary,sum(salary) over(partition by deptName) as sum_salary, avg(salary) over(partition by deptName) as avg_salary, min(salary) over(partition by deptName) as min_salary, max(salary) over(partition by deptName) as max_salary
from data order by deptName
Pandas 类窗口函数代码:
NewPDF = PDF.copy()
WindowPDF = NewPDF.groupby('deptName')['salary'];
NewPDF['sum_salary'] = WindowPDF.transform('sum')
NewPDF['min_salary'] = WindowPDF.transform('min')
NewPDF['mean_salary'] = WindowPDF.transform('mean')
NewPDF['max_salary'] = WindowPDF.transform('max')
NewPDF.sort_values('deptName')print("[Message] Functions Similar to OLAP for Standard Aggregation Based on Pandas DataFrame (Such as min, max, Avg, etc.):")
print(NewPDF.sort_values('deptName'))
输出:
[Message] Functions Similar to OLAP for Standard Aggregation Based on Pandas DataFrame (Such as min, max, Avg, etc.):deptName employeeName salary sum_salary min_salary mean_salary max_salary
2 产品部 王五 12000 33000 9000 11000.000000 12000
3 产品部 赵六 9000 33000 9000 11000.000000 12000
7 产品部 赵敏 12000 33000 9000 11000.000000 12000
0 研发部 张三 10000 31900 8900 10633.333333 13000
1 研发部 李四 13000 31900 8900 10633.333333 13000
6 研发部 张凯 8900 31900 8900 10633.333333 13000
4 项目部 李明 12500 21000 8500 10500.000000 12500
5 项目部 赵亮 8500 21000 8500 10500.000000 12500
Pandas 类窗口排序函数
排序函数常用于对分组集或者整体数据进行排名:
-
row_number: 对分组內的数据进行 “同分不同级” 方式排序, 不存在序号并列的现象, 即使同分时排序也会不同。
-
rank: 对分组內的数据进行 “同分同级且不紧密” 方式排序, 当同分时序号相同, 其它排序按正常排名进行排序, 即 1, 2, 2, 4, 5。
-
dense_rank: 对分组內的数据进行 “同分同级且紧密” 方式排序, 当同分时序号相同, 其它排序按下一排名进行排序, 即 1, 2, 2, 3, 4。
SQL 等效语句:
select deptName, employeeName, salary,row_number(salary) over(partition by deptName order by salary desc) as row_number,rank(salary) over(partition by deptName order by salary desc) as rank,dense_rank(salary) over(partition by deptName order by salary desc) as dense_rank
from data order by employeeName,salary
Pandas 类窗口函数代码:
NewPDF = PDF.copy()
WindowDF = NewPDF.groupby('deptName')['salary'];
NewPDF['row_number'] = WindowPDF.rank(ascending=False,method='first')
NewPDF['rank'] = WindowPDF.rank(ascending=False,method='min')
NewPDF['dense_rank'] = WindowPDF.rank(ascending=False,method='dense')
NewPDF.sort_values(['deptName','salary'])print("[Message] Functions Similar to OLAP for Sorting Based on Pandas DataFrame:")
print(NewPDF.sort_values(['deptName','salary']))
输出:
[Message] Functions Similar to OLAP for Sorting Based on Pandas DataFrame:deptName employeeName salary row_number rank dense_rank
3 产品部 赵六 9000 3.0 3.0 2.0
2 产品部 王五 12000 1.0 1.0 1.0
7 产品部 赵敏 12000 2.0 1.0 1.0
6 研发部 张凯 8900 3.0 3.0 3.0
0 研发部 张三 10000 2.0 2.0 2.0
1 研发部 李四 13000 1.0 1.0 1.0
5 项目部 赵亮 8500 2.0 2.0 2.0
4 项目部 李明 12500 1.0 1.0 1.0
Pandas 类窗口分布函数
在 SQL 中分布函数主要分为两类: percent_rank() 和 cume_dist():
-
percent_rank(): 指按照排名计算百分比, 即该排名位于区间[0,1]的位置, 其中区间内第一名为值0, 最后一名值为1。其具体公式为: percent_rank() = (rank - 1) / (rows - 1)
-
cume_dist(): 指区间內大于等于当前排名的行数占区间内总函数的比例。多用于判断比当前薪资、得分高的用户比例为多少。
SQL 等效语句:
select deptName, employeeName, salary,percent_rank(salary) over(partition by deptName order by salary desc) as percent_rank,cume_dist(salary) over(partition by deptName order by salary desc) as cume_dist
from data order by employeeName,salary
Pandas 类窗口函数代码:
NewPDF = PDF.copy()
WindowPDF = NewPDF.groupby('deptName')['salary'];
NewPDF['rank'] = WindowPDF.rank(ascending=False,method='min')
NewPDF['count'] = WindowPDF.transform('size')
NewPDF['percent_rank'] = (WindowPDF.rank(ascending=False,method='min')-1) / (WindowPDF.transform('count')-1) # -> 如果分组只有一个记录则数据为 na。
NewPDF['cume_dist'] = WindowPDF.rank(ascending=False,method='first',pct=True) # -> 可以结合排序函数的方法使用。
NewPDF.sort_values(['deptName','salary'])print("[Message] Functions Similar to OLAP for Cumulative Distribution Based on Pandas DataFrame:")
print(NewPDF.sort_values(['deptName','salary']))
输出:
[Message] Functions Similar to OLAP for Cumulative Distribution Based on Pandas DataFrame:deptName employeeName salary rank count percent_rank cume_dist
3 产品部 赵六 9000 3.0 3 1.0 1.000000
2 产品部 王五 12000 1.0 3 0.0 0.333333
7 产品部 赵敏 12000 1.0 3 0.0 0.666667
6 研发部 张凯 8900 3.0 3 1.0 1.000000
0 研发部 张三 10000 2.0 3 0.5 0.666667
1 研发部 李四 13000 1.0 3 0.0 0.333333
5 项目部 赵亮 8500 2.0 2 1.0 1.000000
4 项目部 李明 12500 1.0 2 0.0 0.500000
Pandas 类窗口平移函数
在 SQL 中平移函数主要分为两类: lead(列名, n) 和 lag(列名, n), 此函数多用于计算指标同比、环比:
-
lead(列名, n): 获取分区內向下平移n行数据。
-
lag(列名, n): 获取分区內向上平移n行数据。
SQL 等效语句:
select deptName, employeeName, salary,lead(salary,1) over(partition by deptName order by salary desc ) as lead,lag(salary,1) over(partition by deptName order by salary desc) as lag
from data order by deptName,salary desc
Pandas 类窗口函数代码:
NewPDF = PDF.copy()
NewPDF['lead'] = NewPDF.sort_values(['deptName','salary'],ascending=False).groupby('deptName')['salary'].shift(-1) # 分区內向下平移一个单位。
NewPDF['lag'] = NewPDF.sort_values(['deptName','salary'],ascending=False).groupby('deptName')['salary'].shift(1) # 分区內向上平移一个单位。
NewPDF.sort_values(['deptName','salary'],ascending=False)print("[Message] Functions Similar to OLAP for Parallel Movement Based on Pandas DataFrame:")
print(NewPDF.sort_values(['deptName','salary'],ascending=False))
输出:
[Message] Functions Similar to OLAP for Parallel Movement Based on Pandas DataFrame:deptName employeeName salary lead lag
4 项目部 李明 12500 8500.0 NaN
5 项目部 赵亮 8500 NaN 12500.0
1 研发部 李四 13000 10000.0 NaN
0 研发部 张三 10000 8900.0 13000.0
6 研发部 张凯 8900 NaN 10000.0
2 产品部 王五 12000 12000.0 NaN
7 产品部 赵敏 12000 9000.0 12000.0
3 产品部 赵六 9000 NaN 12000.0
Pandas 类窗口首尾函数
在 SQL 中首尾函数主要分为两类: first_val() 和 last_val():
-
first_val(): 获取分区內第一行数据。
-
last_val(): 获取分区內最后一行数据。
SQL 等效语句:
select deptName, employeeName, salary,first_val(salary) over(partition by deptName order by salary desc ) as first_val,-- 由于窗口函数默认的是第一行至当前行, 所以在使用last_val()函数时, 会出现分区内最后一行和当前行大小一致的情况, 因此我们需要将分区偏移量改为第一行至最后一行。 last_val(salary) over(partition by deptName order by salary desc rows between UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING) as last_val
from data order by deptName,salary
Pandas 类窗口函数代码:
NewPDF = PDF.copy()
NewPDF['first_val'] = NewPDF.groupby('deptName')['salary'].transform('min')
NewPDF['last_val'] = NewPDF.groupby('deptName')['salary'].transform('max')
NewPDF.sort_values(['deptName','salary'],ascending=True)print("[Message] Functions Similar to OLAP for Head and Tail Based on Pandas DataFrame:")
print(NewPDF.sort_values(['deptName','salary'],ascending=True))
输出:
[Message] Functions Similar to OLAP for Head and Tail Based on Pandas DataFrame:deptName employeeName salary first_val last_val
3 产品部 赵六 9000 9000 12000
2 产品部 王五 12000 9000 12000
7 产品部 赵敏 12000 9000 12000
6 研发部 张凯 8900 8900 13000
0 研发部 张三 10000 8900 13000
1 研发部 李四 13000 8900 13000
5 项目部 赵亮 8500 8500 12500
4 项目部 李明 12500 8500 12500
Pandas 类窗口 Top N 函数
Top n rows per group 每组取 top N。
如果 tips.csv 没有下载到本地, 可以使用如下语句远程读取数据:
url = ("https://raw.github.com/pandas-dev/pandas/main/pandas/tests/io/data/csv/tips.csv")
tips = pd.read_csv(url)
或者点击 CSV数据-Pandas-Tests-IO-Data-CSV-Tips-2024-01-09.zip 下载数据。
按天统计给小费最高的 2 笔记录 (基于餐厅消费数据)
SQL 等效语句:
SELECT * FROM (SELECTt.*,ROW_NUMBER() OVER(PARTITION BY day ORDER BY total_bill DESC) AS rnFROM tips t
)
WHERE rn < 3
ORDER BY day, rn;
Pandas 类窗口函数代码:
tips = pd.read_csv("./tips.csv")# 方式一。
res = tips.assign(rn=tips.sort_values(["total_bill"], ascending=False).groupby(["day"]).cumcount()+ 1
).query("rn < 3").sort_values(["day", "rn"])# 方式二。
# res = tips.assign(
# rnk=tips.groupby(["day"])["total_bill"].rank(
# method="first", ascending=False
# )
# ).query("rnk < 3").sort_values(["day", "rnk"])print("[Message] Functions Similar to OLAP for The Top N by Day Based on Pandas DataFrame:")
print(res)
输出:
[Message] Functions Similar to OLAP for The Top N by Day Based on Pandas DataFrame:total_bill tip sex smoker day time size rnk95 40.17 4.73 Male Yes Fri Dinner 4 1.090 28.97 3.00 Male Yes Fri Dinner 2 2.0
170 50.81 10.00 Male Yes Sat Dinner 3 1.0
212 48.33 9.00 Male No Sat Dinner 4 2.0
156 48.17 5.00 Male No Sun Dinner 6 1.0
182 45.35 3.50 Male Yes Sun Dinner 3 2.0
197 43.11 5.00 Female Yes Thur Lunch 4 1.0
142 41.19 5.00 Male No Thur Lunch 5 2.0
按性别统计给小费最高的 2 笔记录 (基于餐厅消费数据)
SQL 等效语句:
SELECT * FROM (SELECTt.*,RANK() OVER(PARTITION BY sex ORDER BY tip desc) AS rnkFROM tips tWHERE tip < 2
)
WHERE rnk < 3
ORDER BY sex, rnk;
Pandas 类窗口函数代码:
tips = pd.read_csv("./tips.csv")print("[Message] Functions Similar to OLAP for The Top N by Sex Based on Pandas DataFrame:")
(tips.assign(rnk_min=tips.groupby(["sex"])["tip"].rank(method="min",ascending=False)).query("rnk_min < 3").sort_values(["sex", "rnk_min"],ascending=True)
)
输出:
[Message] Functions Similar to OLAP for The Top N by Sex Based on Pandas DataFrame:total_bill tip sex smoker day time size rnk_min
214 28.17 6.5 Female Yes Sat Dinner 3 1.052 34.81 5.2 Female No Sun Dinner 4 2.0
170 50.81 10.0 Male Yes Sat Dinner 3 1.0
212 48.33 9.0 Male No Sat Dinner 4 2.0
nlargest 的使用示例 (基于餐厅消费数据)
SQL 等效语句:
SELECT * FROM tips ORDER BY tip DESC LIMIT 10 OFFSET 5;
Pandas 类窗口函数代码:
tips = pd.read_csv("./tips.csv")res = tips.nlargest(10 + 5, columns="tip").tail(10)print("[Message] Functions Similar to OLAP for The Top N by nlargest Based on Pandas DataFrame:")
print(res)
输出:
[Message] Functions Similar to OLAP for The Top N by nlargest Based on Pandas DataFrame:total_bill tip sex smoker day time size
183 23.17 6.50 Male Yes Sun Dinner 4
214 28.17 6.50 Female Yes Sat Dinner 347 32.40 6.00 Male No Sun Dinner 4
239 29.03 5.92 Male No Sat Dinner 388 24.71 5.85 Male No Thur Lunch 2
181 23.33 5.65 Male Yes Sun Dinner 244 30.40 5.60 Male No Sun Dinner 452 34.81 5.20 Female No Sun Dinner 485 34.83 5.17 Female No Thur Lunch 4
211 25.89 5.16 Male Yes Sat Dinner 4
总结
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