What does the for loop do in the following code?

Question

I am trying to learn scikit learn (sklearn). Following is a part of code trying to create a data frame with statsmodels.api from iris dataset. But I'm not sure how the for loop works and the datatypes of iris.target_names[x] & target from sci-kit. Can anyone please explain?

from sklearn import datasets ## Get dataset from sklearn

## Import the dataset from sklearn.datasets
iris = datasets.load_iris()

## Create a data frame from the dictionary
species = [iris.target_names[x] for x in iris.target]

It is a list comprehension: https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions — LeKhan9, Jul 09 '19 at 17:43
Possible duplicate of [What does "list comprehension" mean? How does it work and how can I use it?](https://stackoverflow.com/questions/34835951/what-does-list-comprehension-mean-how-does-it-work-and-how-can-i-use-it) — wjandrea, Jul 09 '19 at 17:44

Duncan McFarlane · Answer 1 · 2019-07-09T20:18:14.590

2

This is functionally equivalent to the following:

species = []
for x in iris.target:
    species.append(iris.target_names[x])

In essence it is applying a function on every element x in the iterable and creating a list out of the results.

Performing an operation over a list this way is slightly faster than the previously mentioned method and is more readable (in my opinion).

edited Jul 09 '19 at 20:18

answered Jul 09 '19 at 17:44

Duncan McFarlane

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furas · Accepted Answer · 2019-07-09T17:49:33.480

1

It is list comprehension and it do

species = []

for x in iris.target:
    val = iris.target_names[x]
    species.append(val)

for gets values one-by-one from column iris.targetand assigns to x and then it use this x to get value from column iris.target_names and appends this value on list `species.

So it converts values target to values target_name

edited Jul 09 '19 at 17:49

answered Jul 09 '19 at 17:42

furas

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What does the for loop do in the following code?

2 Answers2