如何合並 Pandas 中的列？

Question

我有一個數據幀index_crisis並且想要創建一個新列，當索引達到本地峰值時包含 1，否則為 0。 我不知道如何繼續我的代碼。 列表peak locations是： [ 2 7 9 13 16 18 21] 但有了month[peak_locations]我得到了峰值的月份。

    Date           Index 
38  2007-06-01  -0.56
39  2007-07-01  -0.36
40  2007-08-01  0.68
41  2007-09-01  0.24
42  2007-10-01  0.22
43  2007-11-01  0.89
44  2007-12-01  0.95
45  2008-01-01  1.53
46  2008-02-01  1.01
47  2008-03-01  1.73
48  2008-04-01  1.39
49  2008-05-01  0.96
50  2008-06-01  1.26
51  2008-07-01  2.37
52  2008-08-01  1.57
53  2008-09-01  2.95
54  2008-10-01  5.7
55  2008-11-01  5.29
56  2008-12-01  5.42
57  2009-01-01  4.99
58  2009-02-01  4.45
59  2009-03-01  4.59
60  2009-04-01  4.2
61  2009-05-01  3.12
62  2009-06-01  1.85

我的預期輸出是一個列dummy ，看起來像：

0
0
1
0
0
0
0
1
0
1
0
0
0
1
0
0
1
0
1
0
0
1
0
0
0

df = pd.read_csv("index_crisis.csv", parse_dates=True)

df['Date'] = pd.to_datetime(df['Date'])
df['Date'] = pd.PeriodIndex(df.Date, freq='M').strftime("%b %Y")


data = df['Index'].values
doublediff = np.diff(np.sign(np.diff(data)))
peak_locations = np.where(doublediff == -2)[0] + 1

Answer 1

idx = df.iloc[peak_locations].index
df['dummy'] = np.where(df.index.isin(idx), 1, 0)

    Date    Index   dummy
38  Jun 2007    -0.56   0
39  Jul 2007    -0.36   0
40  Aug 2007    0.68    1
41  Sep 2007    0.24    0
42  Oct 2007    0.22    0
43  Nov 2007    0.89    0
44  Dec 2007    0.95    0
45  Jan 2008    1.53    1
46  Feb 2008    1.01    0
47  Mar 2008    1.73    1
48  Apr 2008    1.39    0
49  May 2008    0.96    0
50  Jun 2008    1.26    0
51  Jul 2008    2.37    1
52  Aug 2008    1.57    0
53  Sep 2008    2.95    0
54  Oct 2008    5.7     1
55  Nov 2008    5.29    0
56  Dec 2008    5.42    1
57  Jan 2009    4.99    0
58  Feb 2009    4.45    0
59  Mar 2009    4.59    1
60  Apr 2009    4.2     0
61  May 2009    3.12    0
62  Jun 2009    1.85    0

Answer 2

通過以下條件查找局部最大值：值大於下一個且下一個值不大於下一個：

series = df['Index'].values
s = series > series.shift(1)
df[s & (s != s.shift(-1))]

Answer 3

我認為，要使用numpy的的幻想索引建立你的一和零數組。 序列對象可以用作 Numpy 數組的索引器。

按照您的示例，假設您的 DataFrame 長 62 行。 然后：

>>> peak_locations = [2, 7, 9, 13, 16, 18, 21]  # You generated this
>>> dummy = np.zeros(len(df), dtype=int)        # I assume length 62 in this example
>>> print(dummy)

array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])

>>> dummy[peak_locations] = 1                   # This is the fancy indexing hotness 
>>> dummy

array([0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1,
       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])

>>> df["dummy"] = dummy                         # Adds the new column