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I have a piece of Python code that essentially reduces to the following:
import pandas as pd
months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
l = [1607.8, 1688.17, 1605.66, 1469.03, 1312.65, 1451.74, 1445.26, 1350.94, 1371.27, 1201.6, 1240.59, 1291.43]
# First, construct a empty DataFrame.
df = pd.DataFrame(columns = months, dtype=float)
# Then, keep adding rows to DataFrame given by list l.
df.append([l])
print df
Expected output is:
Jan Feb Mar Apr May Jun Jul Aug \
0 1607.8 1688.17 1605.66 1469.03 1312.65 1451.74 1445.26 1350.94
Sep Oct Nov Dec
0 1371.27 1201.6 1240.59 1291.43
However what I get is the following:
Empty DataFrame
Columns: [Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec]
Index: []
If I replace df.append([l]) with the following, things work fine for me.
df = pd.DataFrame([l], columns = months)
df.columns = months
What am I doing wrong?
589
Append Rows to Empty DataFramepandas. DataFrame. append() function is used to add the rows of other DataFrame to the end of the given DataFrame and return a new DataFrame object. Yields below output.
You can create a DataFrame and append a new row to this DataFrame from dict, first create a Python Dictionary and use append() function, this method is required to pass ignore_index=True in order to append dict as a row to DataFrame, not using this will get you an error.
Example 1: Create an Empty DataFrame To create an empty DataFrame, pass no arguments to pandas. DataFrame() class. In this example, we create an empty DataFrame and print it to the console output. As we have provided no arguments, the columns array is empty and index array is empty.
You can create an empty dataframe by importing pandas from the python library. Later, using the pd. DataFrame(), create an empty dataframe without rows and columns as shown in the below example.
You should use pd.DataFrame.loc to add a row given a list l:
df.loc[len(df.index)+1] = l
The method pd.DataFrame.append is used to append one dataframe, or other appendable object, to an existing dataframe:
DataFrame.append(other, ignore_index=False, verify_integrity=False, sort=None)
Append rows of other to the end of this frame
However, it is more efficient to form a list of lists and then call pd.DataFrame.append just once.
list_of_lists = []
for item in some_iterable:
l = foo(item)
list_of_lists.append(l)
df = df.append(pd.DataFrame(list_of_lists, columns=df.columns))
The reason for this is list.append is cheaper than pd.DataFrame.loc assignment.
168
pd.append() does not happen in place. You need to save the output in order to use it.
38
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