iterrows() producing empty column

Question

I am trying to use iterrows() in a for loop to add data to a new column within a dataframe. However, this sadly produces just a new empty column. I am not entirely sure where I am going wrong here. When you run the code, print(row['Key_words']) output values, so its not like there isn't any data in the new column because there is nothing to add.

I am not sure what's going wrong here. The frustrating part is this has worked just fine for me in the past. I am wondering if there are any revisions to the code/alternative solutions to solve this problem?

Data:

df = pd.DataFrame({'id': {0: 1, 1: 2, 2: 3}, 'name': {0: 'Sandwich Cookies', 1: 'All-Seasons Salt', 2: 'Unsweetened Oolong Tea'}, 'a_id': {0: 'cookies cakes', 1: 'spices seasonings', 2: 'tea'}, 'd_id': {0: 'snacks', 1: 'pantry', 2: 'beverages'}})

Example code:

df['Key_words'] = ''
i = 1
for index, row in df.iterrows():
    row['Key_words'] = list(str(i))
    i = i + 1
    print(row['Key_words'])

df

Iterating over a pandas df is generally speaking not a good idea (performance-wise). What do you want to accomplish? — DocZerø
– DocZerø, Commented Mar 20, 2022 at 13:29
@DocZerø I'm really just trying to add new data to the new column Key_words — neuron
– neuron, Commented Mar 20, 2022 at 13:34
The empty column is created by the first line. If you want to add data to the row in this way you should do df.loc[index, 'Key_words'] = list(str(i)), however, as DocZero mentioned, this is very slow. Beter to first create a list of the data and add that to the data frame in one go — Eelco van Vliet
– Eelco van Vliet, Commented Mar 20, 2022 at 13:36

gtomer · Accepted Answer · 2022-03-20 13:38:02Z

2

Try this:

df['Key_words'] = ''
i = 1
for index, row in df.iterrows():
    df.loc[index, 'Key_words'] = list(str(i))
    i = i + 1
    print(row['Key_words'])

df

answered Mar 20, 2022 at 13:38

gtomer

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DocZerø · Accepted Answer · 2022-03-20 13:50:04Z

1

This should solve the issue without having to resort to iterating row by row. This assumes that your index is as shown in your post (thus starting from 0).

df['key_words'] = df.apply(lambda x: x.name+1, axis=1)

	id	name	a_id	d_id	key_words
0	1	Sandwich Cookies	cookies cakes	snacks	1
1	2	All-Seasons Salt	spices seasonings	pantry	2
2	3	Unsweetened Oolong Tea	tea	beverages	3

answered Mar 20, 2022 at 13:50

DocZerø

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