CODEWITHSUNDEEP
python-3.xpandas
Satyam Anand
Satyam Anand

Reputation: 489

updating column values in pandas based on condition

I need to update the column value based on these conditions

i. if score > 3, set score to 1.
ii. if score <= 2, set score to 0.
iii. if score == 3, drop that row.

Score has the values between 1 to 5

I have written the following code, but all the values is being changed to 0.

reviews.loc[reviews['Score'] > 3, 'Score'] = 1
reviews.loc[reviews['Score'] <= 2, 'Score'] = 0
reviews.drop(reviews[reviews['Score'] == 3].index, inplace = True)

Please point out the mistake am doing in this.

Upvotes: 3

Views: 6102

Answers (1)

jezrael
jezrael

Reputation: 862406

There is logic problem:

reviews = pd.DataFrame({'Score':range(6)})
print (reviews)
   Score
0      0
1      1
2      2
3      3
4      4
5      5

If set all values higher like 3 to 1 it working like need:

reviews.loc[reviews['Score'] > 3, 'Score'] = 1
print (reviews)
   Score
0      0
1      1
2      2
3      3
4      1
5      1

Then all vallues without 3 are set to 0, so also are replaced 1 from reviews['Score'] > 3:

reviews.loc[reviews['Score'] <= 2, 'Score'] = 0
print (reviews)
   Score
0      0
1      0
2      0
3      3
4      0
5      0

Last are removed 3 rows and get only 0 values:

reviews.drop(reviews[reviews['Score'] == 3].index, inplace = True)
print (reviews)
   Score
0      0
1      0
2      0
4      0
5      0

You can change solution:

reviews = pd.DataFrame({'Score':range(6)})
print (reviews)
   Score
0      0
1      1
2      2
3      3
4      4
5      5

First removed 3 by filter all rows not equal to 3 in boolean indexing:

reviews = reviews[reviews['Score'] != 3].copy()

And then are set values to 0 and 1:

reviews['Score'] = (reviews['Score'] > 3).astype(int)
#alternative
reviews['Score'] = np.where(reviews['Score'] > 3, 1, 0)
print (reviews)
   Score
0      0
1      0
2      0
4      1
5      1

EDIT1:

Your solution should be changed with swap lines - first set 0 and then 1 for avoid overwrite values:

reviews.loc[reviews['Score'] <= 2, 'Score'] = 0
reviews.loc[reviews['Score'] > 3, 'Score'] = 1

reviews.drop(reviews[reviews['Score'] == 3].index, inplace = True)
print (reviews)
   Score
0      0
1      0
2      0
4      1
5      1

Upvotes: 3

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