In PANDAS how to get the index of a known value

Question

If we have a known value in a column  how can we get its index-value  For example     In  148   a   pd DataFrame np arange 10  reshape 5 2  columns   c1   c2    In  149   a Out 149         c1  c2 0   0   1 1   2   3 2   4   5            As we know  we can get a value by the index corresponding to it  like this   In  151   a ix 0 1     In  152   a c2 0    In  154   a c2 ix 0     lt --  use index Out 151   1            Out 152   1         Out 154   1             lt --  get value   But how to get the index by value

User · Answer

To get the index by value  simply add   index 0   to the end of a query  This will return the index of the first row of the result     So  applied to your dataframe   In  1   a a  c2      1  index 0      In  2   a a  c1    gt  7  index 0     Out 1   0                            Out 2   4                            Where the query returns more than one row  the additional index results can be accessed by specifying the desired index  e g   index n   In  3   a a  c2    gt   7  index 1      In  4   a  a  c2    gt  1   amp   a  c1    lt  8   index 2    Out 3   4                            Out 4   3

User · Answer

Using the  loc   accessor   In  25   a loc a  c1      8  index 0  Out 25   4   Can also use the get loc   by setting  c1  as the index  This will not change the original dataframe   In  17   a set index  c1   index get loc 8  Out 17   4

User · Answer

I think this may help you   both index and columns of the values   value you are looking for is not duplicated   poz matrix matrix  minv  dropna axis 1 how  all   dropna how  all   value poz iloc 0 0  index poz index item   column poz columns item     you can get its index and column  duplicated   matrix pd DataFrame   1 1   1 np NAN   index   q   g   columns   f   h    matrix Out 83       f    h q  1  1 0 g  1  NaN poz matrix matrix  minv  dropna axis 1 how  all   dropna how  all   index poz stack   index tolist   index Out 87      q    f      q    h      g    f      you will get a list

User · Answer

The other way around using numpy where      import numpy as np import pandas as pd  In  800   df   pd DataFrame np arange 10  reshape 5 2  columns   c1   c2     In  801   df Out 801       c1  c2 0   0   1 1   2   3 2   4   5 3   6   7 4   8   9  In  802   np where df  c1    6  Out 802    array  3      In  803   indices   list np where df  c1    6  0    In  804   df iloc indices  Out 804       c1  c2 3   6   7  In  805   df iloc indices  index Out 805   Int64Index  3   dtype  int64    In  806   df iloc indices  index tolist   Out 806    3

User · Answer

There might be more than one index map to your value  it make more sense to return a list   In  48   a Out 48       c1  c2 0   0   1 1   2   3 2   4   5 3   6   7 4   8   9  In  49   a c1 a c1    8  index tolist   Out 49    4

[indexing] In PANDAS, how to get the index of a known value?

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