I have a list of dataframes like this one :
arr = [df1, df2, df3] And I want to get a position of element in this list:
position_of_df2 = arr.index(df2) But python gives error on this line:
ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all(). What Im doing wrong? PS what is the best way to get index of dataframe in array? Only iteration?
list.index works by checking equality of your input with elements from the list and looking for True. It then returns the index of the first match.
Testing equality of 2 dataframes returns a dataframe:
df1 = pd.DataFrame([[1, 2]]) df2 = pd.DataFrame([[1, 2]]) print(df1 == df2) 0 1 0 True True The truthness of the result is ambiguous:
print(bool(df1 == df2)) # ValueError: The truth value of a DataFrame is ambiguous. # Use a.empty, a.bool(), a.item(), a.any() or a.all(). Option 1
In my opinion, the best way to check if you have the correct dataframe is to use an ordered dictionary and define keys (preferably, use descriptive names as keys):
from collections import OrderedDict o = OrderedDict([(1, df1), (2, df2), (3, df3)]) print(list(o.keys()).index(2)) # 1 Option 2
Use a generator expression with is, which returns True only if 2 variables point to the same object:
lst = [df1, df2, df3] res = next(i for i, j in enumerate(lst) if j is df2) # 1 
is) instead.Based on the answer of @jpp above, also quoting from the answer, https://stackoverflow.com/a/19918849/423725, improvised a solution.
df1 = pandas.DataFrame([1, 2]) df2 = pandas.DataFrame([3, 4]) df3 = pandas.DataFrame([5, 6]) arr = [df1, df2, df3] def isEqual(df1, df2): from pandas.util.testing import assert_frame_equal try: assert_frame_equal(df1, df2) return True except: # appeantly AssertionError doesn't catch all return False def indexDF(df, arr): for index, dataframe in enumerate(arr): if isEqual(df, dataframe): return index indexDF(df2, arr) # 1 
df1 = df2 = pd.DataFrame([[1, 2]]), then both dataframes will be considered the same for indexing purposes. I'm not sure that's what OP wants, but it should be noted.
