pandas - 将 csv 文件转换为 Pandas 数据框

Question

我有一个 CSV 文件，格式如下:

DATES, 01-12-2010, 01-12-2010, 01-12-2010, 02-12-2010, 02-12-2010, 02-12-2010
UNITS, Hz, kV, MW,  Hz, kV, MW
Interval, , , , , ,                                           
00:15, 49.82, 33.73755, 34.65, 49.92, 33.9009, 36.33,
00:30, 49.9, 33.7722, 35.34, 49.89, 33.8382, 37.65,
00:45, 49.94, 33.8316, 33.5, 50.09, 34.07745, 37.41,
01:00, 49.86, 33.94875, 30.91, 50.18,   34.20945, 36.11,
01:15, 49.97, 34.2243,  27.28,  50.11,  34.3596, 33.24,
01:30,  50.02,  34.3332, 26.91, 50.12,  34.452, 31.03,
01:45,  50.01,  34.1286, 31.26, 50, 33.9306, 38.86,
02:00,  50.08,  33.9141, 34.96, 50.14,  33.99165, 38.31,
02:15,  50.07,  33.84975, 35.33, 50.01, 33.9537, 39.78,
02:30,  49.97,  34.0263, 33.63, 50.07,  33.8547, 41.48,

我想将以上内容转换为以下格式的数据框:

                    Hz      kV          MW
DATES_Interval
01-12-2010 00:15    49.82   33.73755    34.65
01-12-2010 00:30    49.9    33.7722     35.34
01-12-2010 00:45    49.94   33.8316     33.5
01-12-2010 01:00    49.86   33.94875    30.91
01-12-2010 01:15    49.97   34.2243     27.28
01-12-2010 01:30    50.02   34.3332     26.91
01-12-2010 01:45    50.01   34.1286     31.26
01-12-2010 02:00    50.08   33.9141     34.96
01-12-2010 02:15    50.07   33.84975    35.33
01-12-2010 02:30    49.97   34.0263     33.63
02-12-2010 00:15    49.92   33.9009     36.33
02-12-2010 00:30    49.89   33.8382     37.65
02-12-2010 00:45    50.09   34.07745    37.41
02-12-2010 01:00    50.09   34.07745    37.41
02-12-2010 01:15    50.11   34.3596     33.24
02-12-2010 01:30    50.12   34.452      31.03
02-12-2010 01:45    50      33.9306     38.86
02-12-2010 02:00    50.14   33.99165    38.31
02-12-2010 02:15    50.01   33.9537     39.78
02-12-2010 02:30    50.07   33.8547     41.48

我如何用 pandas 做到这一点？

Answer 1

在 pandas 中做这种事情的关键是 stack()方法:

df.stack(level=0)

但是，我发现到达一个可以使用它的地方，至少特定的 csv 是棘手的。至少可以这么说(几乎肯定有更好的方法来做到这一点!):

df_data = pd.read_csv('e.csv', sep=',\s+', header=None, skiprows=3)[range(7)].set_index(0)
df_cols = pd.read_csv('e.csv', sep=',\s+', header=None, nrows=2).set_index(0)[:2] #interval causing problems    
df_ = df_cols.append(df_data).T.set_index(['DATES','UNITS','Interval']).T
df = df_.stack(level=0)
df_dates = map(lambda x: pd.to_datetime(' '.join(x[::-1])), df.index)
df.index = df_dates

In [7]: df
Out[7]: 
UNITS                   Hz      MW        kV
2010-01-12 00:15:00  49.82   34.65  33.73755
2010-02-12 00:15:00  49.92  36.33,   33.9009
2010-01-12 00:30:00   49.9   35.34   33.7722
2010-02-12 00:30:00  49.89  37.65,   33.8382
2010-01-12 00:45:00  49.94    33.5   33.8316
2010-02-12 00:45:00  50.09  37.41,  34.07745
2010-01-12 01:00:00  49.86   30.91  33.94875
2010-02-12 01:00:00  50.18  36.11,  34.20945
2010-01-12 01:15:00  49.97   27.28   34.2243
2010-02-12 01:15:00  50.11  33.24,   34.3596
2010-01-12 01:30:00  50.02   26.91   34.3332
2010-02-12 01:30:00  50.12  31.03,    34.452
2010-01-12 01:45:00  50.01   31.26   34.1286
2010-02-12 01:45:00     50  38.86,   33.9306
2010-01-12 02:00:00  50.08   34.96   33.9141
2010-02-12 02:00:00  50.14  38.31,  33.99165
2010-01-12 02:15:00  50.07   35.33  33.84975
2010-02-12 02:15:00  50.01  39.78,   33.9537
2010-01-12 02:30:00  49.97   33.63   34.0263
2010-02-12 02:30:00  50.07  41.48,   33.8547

这有点乱，有些列中有逗号!

def clean(s):
    try: return float(s.strip(','))
    except: return s

In [9]: df.applymap(clean)
Out[9]: 
                        Hz     MW        kV
2010-01-12 00:15:00  49.82  34.65  33.73755
2010-02-12 00:15:00  49.92  36.33  33.90090
2010-01-12 00:30:00  49.90  35.34  33.77220
2010-02-12 00:30:00  49.89  37.65  33.83820
2010-01-12 00:45:00  49.94  33.50  33.83160
2010-02-12 00:45:00  50.09  37.41  34.07745
2010-01-12 01:00:00  49.86  30.91  33.94875
2010-02-12 01:00:00  50.18  36.11  34.20945
2010-01-12 01:15:00  49.97  27.28  34.22430
2010-02-12 01:15:00  50.11  33.24  34.35960
2010-01-12 01:30:00  50.02  26.91  34.33320
2010-02-12 01:30:00  50.12  31.03  34.45200
2010-01-12 01:45:00  50.01  31.26  34.12860
2010-02-12 01:45:00  50.00  38.86  33.93060
2010-01-12 02:00:00  50.08  34.96  33.91410
2010-02-12 02:00:00  50.14  38.31  33.99165
2010-01-12 02:15:00  50.07  35.33  33.84975
2010-02-12 02:15:00  50.01  39.78  33.95370
2010-01-12 02:30:00  49.97  33.63  34.02630
2010-02-12 02:30:00  50.07  41.48  33.85470