How do I create an empty DataFrame, then add rows, one by one? I created an empty DataFrame: df = pd.DataFrame(columns=(‘lib’, ‘qty1’, ‘qty2’)) Then I can add a new row at the end and fill a single field with: df = df._set_value(index=len(df), col=”qty1″, value=10.0) It works for only one field at a time. What is … Read more
I want to convert a table, represented as a list of lists, into a pandas DataFrame. As an extremely simplified example: a = [[‘a’, ‘1.2’, ‘4.2’], [‘b’, ’70’, ‘0.03’], [‘x’, ‘5’, ‘0’]] df = pd.DataFrame(a) What is the best way to convert the columns to the appropriate types, in this case columns 2 and 3 … Read more
I want to get a list of the column headers from a Pandas DataFrame. The DataFrame will come from user input, so I won’t know how many columns there will be or what they will be called. For example, if I’m given a DataFrame like this: >>> my_dataframe y gdp cap 0 1 2 5 … Read more
I have the following DataFrame (df): import numpy as np import pandas as pd df = pd.DataFrame(np.random.rand(10, 5)) I add more column(s) by assignment: df[‘mean’] = df.mean(1) How can I move the column mean to the front, i.e. set it as first column leaving the order of the other columns untouched? 4 42
How do I get the number of rows of a pandas dataframe df? 1 15 For a dataframe df, one can use any of the following: len(df.index) df.shape[0] df[df.columns[0]].count() (== number of non-NaN values in first column) Code to reproduce the plot: import numpy as np import pandas as pd import perfplot perfplot.save( “out.png”, setup=lambda … Read more
I have data in different columns, but I don’t know how to extract it to save it in another variable. index a b c 1 2 3 4 2 3 4 5 How do I select ‘a’, ‘b’ and save it in to df1? Unsuccessful attempt: df1 = df[‘a’:’b’] df1 = df.ix[:, ‘a’:’b’] 2 21 … Read more
When deleting a column in a DataFrame I use: del df[‘column_name’] And this works great. Why can’t I use the following? del df.column_name Since it is possible to access the column/Series as df.column_name, I expected this to work. 1 19
How do I change the column labels of a pandas DataFrame from: [‘$a’, ‘$b’, ‘$c’, ‘$d’, ‘$e’] to [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]. 3 32 RENAME SPECIFIC COLUMNS Use the df.rename() function and refer the columns to be renamed. Not all the columns have to be renamed: df = df.rename(columns={‘oldName1’: ‘newName1’, ‘oldName2’: ‘newName2’}) # Or … Read more
How can I select rows from a DataFrame based on values in some column in Pandas? In SQL, I would use: SELECT * FROM table WHERE column_name = some_value 1 13
I have a DataFrame from Pandas: import pandas as pd inp = [{‘c1’:10, ‘c2’:100}, {‘c1′:11,’c2’:110}, {‘c1′:12,’c2’:120}] df = pd.DataFrame(inp) print df Output: c1 c2 0 10 100 1 11 110 2 12 120 Now I want to iterate over the rows of this frame. For every row I want to be able to access its … Read more