Converting some columns from pandas dataframe to list of lists

Question

I have a dataframe. I would like some of the data to be converted to a list of list. The columns I'm interested in are the index, Name, and Births. My code works, but it seems inefficient and for some reason the letter L is added to the end of each index.

My code:

import pandas as pd


data = [['Bob', 968, 'Male'], ['Jessica', 341, 'Female'], ['Mary', 77, 'Female'], ['John', 578, 'Male'], ['Mel', 434, 'Female']]
headers = ['Names', 'Births', 'Gender']
df = pd.DataFrame(data = data, columns=headers)
indexes = df.index.values.tolist()
mylist =  [[x] for x in indexes]

for x in mylist:
    x.extend([df.ix[x[0],'Names'], df.ix[x[0],'Births']])

print mylist

Desired Output:

[[0, 'Bob', 968], [1, 'Jessica', 341], [2, 'Mary', 77], [3, 'John', 578], [4, 'Mel', 434]]

I just ran your code as is using python 2.7.9 and pandas 0.16.2 and the output was exactly what you want. — Julien Grenier
– Julien Grenier, Commented Jul 7, 2015 at 14:09
@JulienGrenier. Yes I am looking for efficiency improvements to my code. Also the tolist() functionality seems to add an L to the end of things so the actual ouput is: [[0L, 'Bob', 968], [1L, 'Jessica', 341], [2L, 'Mary', 77], [3L, 'John', 578], [4L, 'Mel', 434]] — user2242044
– user2242044, Commented Jul 7, 2015 at 14:21

Jianxun Li · Accepted Answer · 2015-07-07 14:27:42Z

11

Why not just use .values.tolist() as you mentioned?

import pandas as pd

# your data
# =================================================
data = [['Bob', 968, 'Male'], ['Jessica', 341, 'Female'], ['Mary', 77, 'Female'], ['John', 578, 'Male'], ['Mel', 434, 'Female']]
headers = ['Names', 'Births', 'Gender']
df = pd.DataFrame(data = data, columns=headers)

# nested list
# ============================
df.reset_index()[['index', 'Names', 'Births']].values.tolist()

Out[46]: 
[[0, 'Bob', 968],
 [1, 'Jessica', 341],
 [2, 'Mary', 77],
 [3, 'John', 578],
 [4, 'Mel', 434]]

edited Jul 7, 2015 at 14:27

answered Jul 7, 2015 at 14:15

Jianxun Li

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7 Comments

user2242044 Over a year ago

This outputs: [[0L, 'Bob', 968L], [1L, 'Jessica', 341L], [2L, 'Mary', 77L], [3L, 'John', 578L], [4L, 'Mel', 434L]]. Why are the L's being added?

Jianxun Li Over a year ago

@user2242044 L means 'Long' integer. I didn't see that 'L' appended to my output. Let me think about possible causes.

user2242044 Over a year ago

Also is there is an opposite function of drop() such as include? For example say my dataframe had 40 columns and I wanted two of them.

Julien Grenier Over a year ago

@user2242044: First of all, I don't see the L in my shell. Also the L only means that those are longs instead of integers.

Jianxun Li Over a year ago

@user2242044 can you try this df.reset_index()[['index', 'Names', 'Births']].values.astype(str).tolist()? Does it still produce something with L appended?

|

Ohumeronen · Accepted Answer · 2016-07-03 14:47:26Z

2

Ok, this works (based on Jianxun Li's answer and comments):

import pandas as pd

# Data
data = [['Bob', 968, 'Male'], ['Jessica', 341, 'Female'], ['Mary', 77, 'Female'], ['John', 578, 'Male'], ['Mel', 434, 'Female']]
headers = ['Names', 'Births', 'Gender']
df = pd.DataFrame(data = data, columns=headers)

# Output
print df.reset_index()[['index', 'Names', 'Births']].values.astype(str).tolist()

Thank you Jianxun Li, this also helped me :-)

In general, one can use the following to transform the complete dataframe into a list of lists (which is what I needed):

df.values.astype(str).tolist()

edited Jul 3, 2016 at 14:47

answered Jul 3, 2016 at 14:42

Ohumeronen

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