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

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!

CodePudding user response：

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
```

CodePudding user response：

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

CodePudding user response：

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.

CodePudding user response：

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