如何在 pandas.DataFrame 中找到值的位置？

Question

I want to search for 'row3' in the index of the DataFrame below, which should be 2 for a zero-based array.

import numpy as np
import pandas as pd

rownames = ['row1', 'row2', 'row3', 'row4', 'row5']
colnames = ['col1', 'col2', 'col3', 'col4']

# Create a 5 row by 4 column array of integers from 0 to 19
integers = np.arange(20).reshape((5, 4))
table = pd.DataFrame(integers, index=rownames, columns=colnames)

Is there a function which return the row number of 'row3'? Thanks in advance for any help.

Answer 1

You could use Index.get_loc ( docs ):

>>> table.index.get_loc("row3")
2
>>> table.iloc[table.index.get_loc("row3")]
col1     8
col2     9
col3    10
col4    11
Name: row3, dtype: int64
>>> table.loc["row3"]
col1     8
col2     9
col3    10
col4    11
Name: row3, dtype: int64

But this is a somewhat unusual access pattern-- never need it myself.

Answer 2

You may just find the length of df from 'row1' till 'row3' and decrease it by 1 (if you are starting count from 0).

s = 'row3'
print(s,'number is', len(table['row1':s]) - 1)

returns

row3 number is 2