How do I convert a pandas Series or index to a Numpy array

Question

Do you know how to get the index or column of a DataFrame as a NumPy array or python list

User · Answer

You can use df index to access the index object and then get the values in a list using df index tolist    Similarly  you can use df  col   tolist   for Series

User · Answer

A more recent way to do this is to use the  to numpy   function   If I have a dataframe with a column  price   I can convert it as follows   priceArray   df  price   to numpy     You can also pass the data type  such as float or object  as an argument of the function

User · Answer

To get a NumPy array  you should use the values attribute   In  1   df   pd DataFrame   A    1  2  3    B    4  5  6    index   a    b    c     df    A  B a  1  4 b  2  5 c  3  6  In  2   df index values Out 2   array   a    b    c    dtype object    This accesses how the data is already stored  so there s no need for a conversion  Note  This attribute is also available for many other pandas  objects   In  3   df  A   values Out 3   Out 16   array  1  2  3       To get the index as a list  call tolist   In  4   df index tolist   Out 4     a    b    c     And similarly  for columns

User · Answer

I converted the pandas dataframe to list and then used the basic list index    Something like this   dd   list zone 0    Where zone 0  is some specific column of the table idx   dd index filename i     You have you index value as idx

User · Answer

pandas    0 24  Deprecate your usage of  values in favour of these methods   From v0 24 0 onwards  we will have two brand spanking new  preferred methods for obtaining NumPy arrays from Index  Series  and DataFrame objects  they are to numpy    and  array  Regarding usage  the docs mention      We haven   t removed or deprecated Series values or   DataFrame values  but we highly recommend and using  array or    to numpy   instead    See this section of the v0 24 0 release notes for more information      to numpy   Method  df index to numpy     array   a    b    dtype object   df  A   to numpy      array  1  4     By default  a view is returned  Any modifications made will affect the original   v   df index to numpy   v 0    -1  df     A  B -1  1  2 b   4  5   If you need a copy instead  use to numpy copy True    v   df index to numpy copy True  v -1    -123  df    A  B a  1  2 b  4  5   Note that this function also works for DataFrames  while  array does not      array Attribute This attribute returns an ExtensionArray object that backs the Index Series     pd   version      0 24 0rc1     Setup  df   pd DataFrame   1  2    4  5    columns   A    B    index   a    b    df     A  B a  1  2 b  4  5     df index array        lt PandasArray gt      a    b     Length  2  dtype  object  df  A   array    lt PandasArray gt     1  4    Length  2  dtype  int64   From here  it is possible to get a list using list   list df index array      a    b    list df  A   array     1  4    or  just directly call  tolist     df index tolist       a    b    df  A   tolist      1  4    Regarding what is returned  the docs mention      For Series and Indexes backed by normal NumPy arrays  Series array   will return a new arrays PandasArray  which is a thin  no-copy    wrapper around a numpy ndarray  arrays PandasArray isn   t especially   useful on its own  but it does provide the same interface as any   extension array defined in pandas or by a third-party library    So  to summarise   array will return either   The existing ExtensionArray backing the Index Series  or  If there is a NumPy array backing the series  a new ExtensionArray object is created as a thin wrapper over the underlying array       Rationale for adding TWO new methods These functions were added as a result of discussions under two GitHub issues GH19954 and GH23623    Specifically  the docs mention the rationale            with  values it was unclear whether the returned value would be the   actual array  some transformation of it  or one of pandas custom   arrays  like Categorical   For example  with PeriodIndex   values   generates a new ndarray of period objects each time          These two functions aim to improve the consistency of the API  which is a major step in the right direction   Lastly   values will not be deprecated in the current version  but I expect this may happen at some point in the future  so I would urge users to migrate towards the newer API  as soon as you can

User · Answer

If you are dealing with a multi-index dataframe  you may be interested in extracting only the column of one name of the multi-index  You can do this as  df index get level values  name sub index     and of course name sub index must be an element of the FrozenList df index names

User · Answer

Below is a simple way to convert dataframe column into numpy array   df   pd DataFrame somedict   ytrain   df  label   ytrain numpy   np array  x for x in ytrain  label       ytrain numpy  is a numpy array   I tried with to numpy   but it gave me the below error  TypeError  no supported conversion for types   dtype  O     while doing Binary Relevance classfication using Linear SVC  to numpy   was converting the dataFrame into numpy array but the inner element s data type was list because of which the above error was observed

User · Answer

Since pandas v0 13 you can also use get values   df index get values

[python] How do I convert a pandas Series or index to a Numpy array?

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