Python-科学计算-pandas-22-按某列排序

zishendianxia

发布于 2021-09-29 15:52:57

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发布于 2021-09-29 15:52:57

文章被收录于专栏：Python工程师Python工程师

系统：Windows 10 编辑器：JetBrains PyCharm Community Edition 2018.2.2 x64 pandas：1.1.5

这个系列讲讲Python的科学计算及可视化
今天讲讲pandas模块
将df按某列进行排序

Part 1：场景描述

已知df1，包括6列，"time", "pos", "value1", "value2", "value3", "value4
其中value4为周次信息，想获取最新周次value1的取值
如下图，最新的周次应该为21KW36，其对应value1的取值为50

Part 2：逻辑

将df按照value4列进行排序
取第1行value1的取值即为所求

Part 3：代码

import pandas as pd

dict_1 = {"time": ["2019-11-02", "2019-11-03", "2019-11-04", "2019-11-05",
                   "2019-12-02", "2019-12-03", "2019-12-04", "2019-12-05"],
          "pos": ["A", "A", "C", "D", "E", "E", "G", "H"],
          "value1": [10, 20, 30, 40, 50, 50, 70, 80],
          "value2": [100, 200, 300, 400, 500, 600, 700, 800],
          "value3": [50, 20, 30, 90, 50, 60, 80, 80],
          "value4": ['21W12', '21W10', '21W01', '21W05', '21W06', '21W36', '21W21', '21W23']}

df_1 = pd.DataFrame(dict_1, columns=["time", "pos", "value1", "value2", "value3", "value4"])
print("\n", "df_1", "\n", df_1, "\n")

df_1.sort_values(by='value4', ascending=False, inplace=True)

print("\n", "排序后df_1", "\n", df_1, "\n")
# 第1行第3列
val = df_1.iloc[0, 2]
remarks = "最新周value1取值：{0}".format(val)

print(remarks)

代码截图

执行结果

Part 4：部分代码解读

df_1.sort_values(by='value4', ascending=False, inplace=True)，将df_1按照value4列进行排序，且排序方法为降序，ascending=False表示为降序，ascending为上升的意思
- df_1.sort_values(by='value4', ascending=True, inplace=True)即按照升序来排序，结果如下图
val = df_1.iloc[0, 2]，获取第1行第3列的取值，即value1列的取值。iloc为按照位置来取值，注意与loc的区别