Pandas: Checking and changing all items in a column

Question

i try to run a code where i go through a column in a pandas dataframe like that:

for item in df['delta']:
    if float(item) < 0:
        print(item)

Whenever i detect an item with a value below 0, i want to add 1,000,000 and put the result back into the dataframe.

I tried something like:

df['delta'][item] = float(item) + 1000000

but then i get a key error.

How can i access the current location of the for-loop?

the answer to this question is already present: https://stackoverflow.com/questions/31569384/set-value-for-particular-cell-in-pandas-dataframe-with-iloc — Roberto Bellarosa, Dec 03 '19 at 16:26
This is Pandas 101. Have you made any effort whatsoever to solve this yourself?! Please see: [ask], https://meta.stackoverflow.com/questions/261592/how-much-research-effort-is-expected-of-stack-overflow-users. — AMC, Dec 03 '19 at 17:16

score 2 · Answer 1 · answered Dec 03 '19 at 16:34

Suppose you have

    df = pd.DataFrame({'col_1': [0,1,2,3,4,5,-1,-2,-3]})

You can simply use loc and += operator to have

df.loc[df['col_1'] < 0, 'col_1'] += 10

score 0 · Answer 2 · answered Dec 03 '19 at 16:37

0

I'd recommend using the built-in apply() function for this:

df['delta'] = df['delta'].apply( lambda item: float(item) + 1000000 if float(item) < 0 else item )

answered Dec 03 '19 at 16:37

jackaloops

2 Answers2