python – Pandas pytable：如何指定MultiIndex元素的min_itemsize

我将pandas数据帧存储为包含MultiIndex的pytable.

MultiIndex的第一级是对应于userID的字符串.现在,大多数userID长度为13个字符,但其中一些长度为15个字符.当我追加包含long userID的记录时,pytables会引发错误,因为它需要13个字符的字段.

ValueError('Trying to store a string with len [15] in [user] column but\nthis column has a limit of [13]!\nConsider using min_itemsize to preset the sizes on these columns',)

但是,我不知道如何为MultiIndex的元素设置属性min_itemsize.我试过{‘index’：15}并且它不起作用……

我知道我可以通过添加空格强制所有ID从头开始长达15个字符,但我希望尽可能避免这种情况.

谢谢您的帮助！

解决方法:

您需要指定要为其设置min_itemsize的多索引级别的名称.这是一个例子：

创建2个多索引帧

In [1]: df1 = DataFrame(np.random.randn(4,2),index=MultiIndex.from_product([['abcdefghijklm','foo'],[1,2]],names=['string','number']))

In [2]: df2 = DataFrame(np.random.randn(4,2),index=MultiIndex.from_product([['abcdefghijklmop','foo'],[1,2]],names=['string','number']))

In [3]: df1
Out[3]: 
                             0         1
string        number                    
abcdefghijklm 1       0.737976  0.840718
              2       0.605763  1.797398
foo           1       1.589278  0.104186
              2       0.029387  1.417195

[4 rows x 2 columns]

In [4]: df2
Out[4]: 
                               0         1
string          number                    
abcdefghijklmop 1       0.539507 -1.059085
                2       1.263722 -1.773187
foo             1       1.625073  0.078650
                2      -0.030827 -1.691805

[4 rows x 2 columns]

创建一个商店

In [9]: store = pd.HDFStore('test.h5',mode='w')

In [10]: store.append('df1',df1)

这是计算长度的

In [12]: store.get_storer('df1').table
Out[12]: 
/df1/table (Table(4,)) ''
  description := {
  "index": Int64Col(shape=(), dflt=0, pos=0),
  "values_block_0": Float64Col(shape=(2,), dflt=0.0, pos=1),
  "number": Int64Col(shape=(), dflt=0, pos=2),
  "string": StringCol(itemsize=13, shape=(), dflt='', pos=3)}
  byteorder := 'little'
  chunkshape := (1456,)
  autoindex := True
  colindexes := {
    "index": Index(6, medium, shuffle, zlib(1)).is_csi=False,
    "number": Index(6, medium, shuffle, zlib(1)).is_csi=False,
    "string": Index(6, medium, shuffle, zlib(1)).is_csi=False}

这是你现在得到的错误

In [13]: store.append('df1',df2)

ValueError: Trying to store a string with len [15] in [string] column but
this column has a limit of [13]!
Consider using min_itemsize to preset the sizes on these columns

使用级别名称指定min_itemsize

In [14]: store.append('df',df1,min_itemsize={ 'string' : 15 })

In [15]: store.get_storer('df').table
Out[15]: 
/df/table (Table(4,)) ''
  description := {
  "index": Int64Col(shape=(), dflt=0, pos=0),
  "values_block_0": Float64Col(shape=(2,), dflt=0.0, pos=1),
  "number": Int64Col(shape=(), dflt=0, pos=2),
  "string": StringCol(itemsize=15, shape=(), dflt='', pos=3)}
  byteorder := 'little'
  chunkshape := (1394,)
  autoindex := True
  colindexes := {
    "index": Index(6, medium, shuffle, zlib(1)).is_csi=False,
    "number": Index(6, medium, shuffle, zlib(1)).is_csi=False,
    "string": Index(6, medium, shuffle, zlib(1)).is_csi=False}

附加

In [16]: store.append('df',df2)

In [19]: store.df
Out[19]: 
                               0         1
string          number                    
abcdefghijklm   1       0.737976  0.840718
                2       0.605763  1.797398
foo             1       1.589278  0.104186
                2       0.029387  1.417195
abcdefghijklmop 1       0.539507 -1.059085
                2       1.263722 -1.773187
foo             1       1.625073  0.078650
                2      -0.030827 -1.691805

[8 rows x 2 columns]

In [20]: store.close()

标签：python,pandas,pytables
来源： https://codeday.me/bug/20190929/1832938.html