How do I change the value in a column given a Boolean (in Python)?

Question

In a data frame, when the value of a given column is below 10, I need to change all the values till the end of the column to 5.

so let's say these are the values of the column:

I would need it to become:

I apologize if I didn't explain this well, I'm new to coding. Thanks for all the help!

Answer 1

You can compare the column value with 10 and get the cummax of boolean series to ensure the value after first True is True

df['out'] = df['col'].mask(df['col'].lt(10).cummax().eq(1), 5)

print(df)

   col  out
0  134  134
1  413  413
2   12   12
3   81   81
4    9    5
5  483    5
6   93    5
7   30    5

Answer 2

Let df = pd.DataFrame({'x': [134, 413, 12, 81, 9, 483, 93, 30, 6]}) .

Find the elements that are less than 10: df['x'] < 10
Find the row that contains the first of them: (df['x'] < 10).argmax()
Change that row and all the following rows to 5
```
 df.loc[(df['x'] < 10).argmax():, 'x'] = 5
```

Answer 3

you coutd try: myDataFrame = np.where(myDataFrame < 10, 5, myDataFrame)

this checks where the value is lower than ten. if it is it sets it to five, else it just sets the value to what it already was.

Answer 4

Let's assume the dataframe id df and the column name is x

col_list = df['x'].to_list()
for i in range(len(col_list)):
    if col_list[i] < 10:
        col_list[i] = 5
df['x'] = col_list