Access index of last element in data frame

Question

I ve looking around for this but I can t seem to find it  though it must be extremely trivial    The problem that I have is that I would like to retrieve the value of a column for the first and last entries of a data frame  But if I do   df ix 0   date     I get   datetime datetime 2011  1  10  16  0    but if I do   df -1    date     I get   myIndex 13         2011-12-20 16 00 00 Name  mydate   with a different format  Ideally  I would like to be able to access the value of the last index of the data frame  but I can t find how   I even tried to create a column  IndexCopy  with the values of the index and try   df ix df tail 1   IndexCopy     mydate     but this also yields a different format  since df tail 1   IndexCopy   does not output a simple integer     Any ideas

User · Answer

df tail 1  index    seems the most readable

User · Answer

You want  iloc with double brackets   import pandas as pd df   pd DataFrame   date   range 10  64  8    not date    fools    df index    17 df iloc  0 -1     date      You give  iloc a list of indexes - specifically the first and last   0  -1   That returns a dataframe from which you ask for the  date  column    date   will give you a series  yuck   and    date    will give you a dataframe

User · Answer

Combining  comte s answer and dmdip s answer in Get index of a row of a pandas dataframe as an integer  df tail 1  index item     gives you the value of the index     Note that indices are not always well defined not matter they are multi-indexed or single indexed  Modifying dataframes using indices might result in unexpected behavior  We will have an example with a multi-indexed case but note this is also true in a single-indexed case    Say we have   df   pd DataFrame   x   1 1 3 3    y   3 3 5 5    index  11 11 12 12   stack    11  x    1     y    3     x    1     y    3 12  x    3     y    5                the index is  12   y       x    3     y    5                the index is also  12   y    df tail 1  index item     gives  12   y     Trying to access the last element with the index df 12   y   yields    12  y     5  12  y     5 dtype  int64   If you attempt to modify the dataframe based on the index  12  y   you will modify two rows rather than one  Thus  even though we learned to access the value of last row s index  it might not be a good idea if you want to change the values of last row based on its index as there could be many that share the same index  You should use df iloc -1  to access last row in this case though   Reference  https   pandas pydata org pandas-docs stable generated pandas Index item html

User · Answer

It may be too late now   I use index method to retrieve last index of a DataFrame  then use  -1  to get the last values   For example   df   pd DataFrame np zeros  4  1    columns   A    print f df  n df  n    print f Index    df index  n   print f Last index    df index -1       The output is  df       A 0  0 0 1  0 0 2  0 0 3  0 0  Index   RangeIndex start 0  stop 4  step 1   Last index   3

User · Answer

The former answer is now superseded by  iloc    gt  gt  gt  df   pd DataFrame   date   range 10  64  8     gt  gt  gt  df index    17  gt  gt  gt  df     date 17    10 18    18 19    26 20    34 21    42 22    50 23    58  gt  gt  gt  df  date   iloc 0  10  gt  gt  gt  df  date   iloc -1  58     The shortest way I can think of uses  iget      gt  gt  gt  df   pd DataFrame   date   range 10  64  8     gt  gt  gt  df index    17  gt  gt  gt  df     date 17    10 18    18 19    26 20    34 21    42 22    50 23    58  gt  gt  gt  df  date   iget 0  10  gt  gt  gt  df  date   iget -1  58   Alternatively    gt  gt  gt  df  date   df index 0   10  gt  gt  gt  df  date   df index -1   58   There s also  first valid index   and  last valid index    but depending on whether or not you want to rule out NaNs they might not be what you want   Remember that df ix 0  doesn t give you the first  but the one indexed by 0   For example  in the above case  df ix 0  would produce   gt  gt  gt  df ix 0  Traceback  most recent call last     File   lt ipython-input-489-494245247e87 gt    line 1  in  lt module gt      df ix 0        KeyError  0

User · Answer

Pandas supports NumPy syntax which allows  df len df  -1   index 0

[python] Access index of last element in data frame

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