Python/Pandas：仅在 string.startswith 特定字符串时应用替换

Question

Using pandas to read an excel file. The following code is working fine for one column:

data["ProtocolTCP"] = data["ProtocolTCP"].str.replace("tcp-", "tcp ")

However, I discovered some cells have the value in the middle of the string and do not want to change those.

How can I just apply the same command to just those string that startswith "tcp-" only?

I think a "lambda" command would work but have a hard time figuring it out. Or perhaps there is a better option than lambda?

Answer 1

You can add ^

data["ProtocolTCP"] = data["ProtocolTCP"].str.replace("^tcp-", "tcp ")

Answer 2

You can use np.where() which performs better than a lambda I think:

data["ProtocolTCP"] = np.where(data["ProtocolTCP"].startswith("tcp-"),data["ProtocolTCP"].str.replace("tcp-","tcp "),data["ProtocolTCP"])

Another option using list comprehension:

data["ProtocolTCP"] = [x.replace("tcp-","tcp ") if x.startswith("tcp-") for x in data["ProtocolTCP"].values]