Is it possible when creating a dataframe from a list, to set the index as one of the values?
import pandas as pd
tmp = [['a', 'a1'], ['b',' b1']]
df = pd.DataFrame(tmp, columns=["First", "Second"])
First Second
0 a a1
1 b b1
And how I'd like it to look:
First Second
a a a1
b b b1
Change it to list before assigning it to index
df.index = list(df["First"])
>>> pd.DataFrame(tmp, columns=["First", "Second"]).set_index('First', drop=False)
First Second
First
a a a1
b b b1
set_axisTo set arbitrary values as the index, best practice is to use set_axis:
df = df.set_axis(['idx1', 'idx2'])
# First Second
# idx1 a a1
# idx2 b b1
set_index (list vs array)It's also possible to pass arbitrary values to set_index, but note the difference between passing a list vs array:
list — set_index assigns these columns as the index:
df.set_index(['First', 'First'])
# Second
# First First
# a a a1
# b b b1
array (Series/Index/ndarray) — set_index assigns these values as the index:
df = df.set_index(pd.Series(['First', 'First']))
# First Second
# First a a1
# First b b1
Note that passing arrays to set_index is very contentious among the devs and may even get deprecated.
df.index directly?Directly modifying attributes is fine and is used often, but using methods has its advantages:
Methods provide better error checking, e.g.:
df = df.set_axis(['idx1', 'idx2', 'idx3'])
# ValueError: Length mismatch: Expected axis has 2 elements, new values have 3 elements
df.index = ['idx1', 'idx2', 'idx3']
# No error despite length mismatch
Methods can be chained, e.g.:
df.some_method().set_axis(['idx1', 'idx2']).another_method()
If you don't want index name:
df = pd.DataFrame(tmp, columns=["First", "Second"], index=[i[0] for i in tmp])
Result:
First Second
a a a1
b b b1
import pandas as pd
tmp = [['a', 'a1'], ['b',' b1']]
df = pd.DataFrame(tmp, columns=["First", "Second"]).set_axis([tmp[0][0],tmp[1][0]])
df
df.index = df.Firstdf.set_index('col_name', inplace=True), if you would like to use an external object like list, pd.Series as your index instead opt-2:df.index = list_1