Python: Creating map with 2 lists

Question

I want to create map data from 2 list data. I have a simple example like below. What I want to do is create 'new_map' data like below. If it contains specific data, the value should be True.

all_s = ['s1', 's2', 's3', 's4']
data = ['s2', 's4']
new_map = {'s1': False, 's2': True, 's3': False, 's4': True}

Are there any smart way (like lambda) to implement this? My python env is 3.X. Of course I can resolve this problem if I use for-iter simply. But I wonder there are better ways.

I can do that! new_map = { s: True if (s in data) else False for s in all_s} — jef
– jef, Commented Sep 9, 2016 at 2:05
See the answers below. True if (s in data) else False is the same as s in data only more verbose. — elethan
– elethan, Commented Sep 9, 2016 at 2:10
Yes I notices your answers are better way. But I wanted to note my solution as my study. Thank you for your comment. — jef
– jef, Commented Sep 9, 2016 at 2:12

David Hoffman · Accepted Answer · 2016-09-09 02:13:46Z

4

This should do it quickly and efficiently in a pythonic manner:

 data_set = set(data)
 new_map = {k: k in data_set for k in all_s}

edited Sep 9, 2016 at 2:13

answered Sep 9, 2016 at 2:01

David Hoffman

2,3931 gold badge18 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

elethan Over a year ago

Arg...beat me by a few seconds. Nice idea to use set() too; I didn't think of that! Although, will the function call make it more expensive?

Bi Rico Over a year ago

There is no benefit to using a set if you build the set inside the comprehension :).

David Hoffman Over a year ago

Sorry I got lazy typing on my smart phone and didn't want another line. I'll update.

jef Over a year ago

Are there any meanings to use set func?

Bi Rico Over a year ago

@jef, k in data_set is faster than k in data if data is large. It's worth using a set if you need to check a large number of keys and data is reasonably large.

|

elethan · Accepted Answer · 2016-09-09 02:07:17Z

2

Try a dict comprehension:

new_map = {i: i in data for i in all_s}

edited Sep 9, 2016 at 2:07

answered Sep 9, 2016 at 2:02

elethan

17.1k10 gold badges70 silver badges97 bronze badges

4 Comments

jef Over a year ago

Thank you. This is very smart

Monica Over a year ago

@elethan Could you spell me out why boolean types (True or False) are return instead of values?

elethan Over a year ago

@Monica here I am setting the value in each key-value pair to i in data. i in data == True if i is a value contained in data and False otherwise, so all the values end up as either True or False. Does that make sense?

Monica Over a year ago

@elethan yes, it does! Thank you for your explanation! :)

Monica · Accepted Answer · 2016-09-09 02:17:16Z

1

I'd use a dictionary comprehension:

x = {i:True if i in data else False for i in all_s}

answered Sep 9, 2016 at 2:17

Monica

1,0703 gold badges18 silver badges39 bronze badges

Collectives™ on Stack Overflow

Python: Creating map with 2 lists

3 Answers 3

6 Comments

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

6 Comments

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related