Proper way to utilize .loc in python's pandas -

when trying change column of numbers object float dtypes using pandas dataframes, receive following warning:

a value trying set on copy of slice dataframe. try using .loc[row_indexer,col_indexer] = value instead

now, code runs fine, proper , intended way avoid warning , still achieve goal of:

df2[col] = df2[col].astype('float')

let noted df2 subset of df1 using condition similar to:

df2 = df1[df1[some col] == value]

use copy method. instead of:

df2 = df1[df1[some col] == value]

just write:

df2 = df1[df1[some col] == value].copy()

initially, df2 slice of df1 , not new dataframe. why, when try modify it, python raises error.

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