My for loop doesn't count values from another column in dataframe

Question

I'm completely lost why my for loop doesn't append the value from another column.

My dataframe looks like this

and my code is like this

i = -1
open_line = []

for line in df["line 1"]:
    idx = i + 1
    if (0 < line < 1000 and df.iloc[idx]["line 2"] < 0):
        open_line.append(df.iloc[idx]["line 2"])
    elif line == 1000 and df.iloc[idx]["line 2"] == 1000:
        open_line.append("NAN")
    elif line == 1000 and 0 < df.iloc[idx]["line 2"] < 1000:
        open_line.append("NAN")
    elif line < 0:
        open_line.append(line)

When I print open_line I get

['NAN', 'NAN', -1]

The problem is when first if statement is passed at row 3 it doesn't append -9 to my list but it just goes on.

Thanks for the help.

Laurent · Accepted Answer · 2022-12-03 16:50:45Z

1

The problem comes from the fact that idx is never incremented.

Replace:

i = -1 with idx = -1
and idx = i + 1 with idx = idx + 1

Then print(open_line) outputs ['NAN', 'NAN', -9, -1, -3, -3]

A more efficient way to do it would be like this:

df.loc[(df["line 1"] > 0) & (df["line 1"] < 1_000), "open_line"] = df.loc[
    (df["line 1"] > 0) & (df["line 1"] < 1_000), "line 2"
]
df.loc[
    (df["line 1"] == 1_000) & (df["line 2"] > 0) & (df["line 2"] <= 1_000), "open_line"
] = "NAN"
df.loc[df["line 1"] < 0, "open_line"] = df.loc[df["line 1"] < 0, "line 1"]

open_line = [i if isinstance(i, str) else int(i) for i in df["open_line"]]

Then print(open_line) outputs ['NAN', 'NAN', -9, -1, -3, -3]

answered Dec 3, 2022 at 16:50

Laurent

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