pandas histogram plot error: ValueError: num must be 1 <= num <= 0, not 1

Question

我正在从 pandas 数据框中绘制一个列的直方图：

%matplotlib notebook
import matplotlib.pyplot as plt
import matplotlib
df.hist(column='column_A', bins = 100)

但出现以下错误：

     62                     raise ValueError(
     63                         "num must be 1 <= num <= {maxn}, not {num}".format(
---> 64                             maxn=rows*cols, num=num))
     65                 self._subplotspec = GridSpec(rows, cols)[int(num) - 1]
     66                 # num - 1 for converting from MATLAB to python indexing

ValueError: num must be 1 <= num <= 0, not 1

有谁知道这个错误是什么意思？谢谢！

Answer 1

问题

当column_A 不包含数字数据时，就会出现您遇到的问题。正如您在下面的 pandas.plotting._core 的摘录中看到的那样，数字数据对于使函数 hist_frame（您调用 DataFrame.hist()）正常工作至关重要。

def hist_frame(data, column=None, by=None, grid=True, xlabelsize=None,
               xrot=None, ylabelsize=None, yrot=None, ax=None, sharex=False,
               sharey=False, figsize=None, layout=None, bins=10, **kwds):
    # skipping part of the code
    # ...
    if column is not None:
        if not isinstance(column, (list, np.ndarray, Index)):
            column = [column]
        data = data[column]
    data = data._get_numeric_data()  # there is no numeric data in the column
    naxes = len(data.columns)  # so the number of axes becomes 0
    # naxes is passed to the subplot generating function as 0 and later determines the number of columns as 0
    fig, axes = _subplots(naxes=naxes, ax=ax, squeeze=False,
                          sharex=sharex, sharey=sharey, figsize=figsize,
                          layout=layout)
    # skipping the rest of the code
    # ...

---

解决方案

1. 如果您的问题是用直方图表示 numeric 数据（但不是 numeric dtype yet），您需要使用pd.to_numeric 或df.astype(a_selected_numeric_dtype) 将您的数据转换为数字，例如'float64'，然后继续执行您的代码。

2. 如果您的问题是用直方图表示一列中的非数字数据，您可以使用以下行调用函数hist_series： df['column_A'].hist(bins=100)。

3. 如果您的问题是用直方图表示 许多列 中的 非数字 数据，您可能会求助于几个选项：

   • 使用matplotlib 并直接创建子图和直方图
   • 至少将 pandas 更新到版本 0.25

Answer 2

通常为 0

mta['penn'] = [mta_bystation[mta_bystation.STATION == "34 ST-PENN STA"], 'Penn Station']
mta['grdcntrl'] = [mta_bystation[mta_bystation.STATION == "GRD CNTRL-42 ST"], 'Grand Central']
mta['heraldsq'] = [mta_bystation[mta_bystation.STATION == "34 ST-HERALD SQ"], 'Herald Sq']
mta['23rd'] = [mta_bystation[mta_bystation.STATION == "23 ST"], '23rd St']
#mta['portauth'] = [mta_bystation[mta_bystation.STATION == "42 ST-PORT AUTH"], 'Port Auth']
#mta['unionsq'] = [mta_bystation[mta_bystation.STATION == "14 ST-UNION SQ"], 'Union Sq']
mta['timessq'] = [mta_bystation[mta_bystation.STATION == "TIMES SQ-42 ST"], 'Ti