Python 熊猫：如果不存在则添加列
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Pandas: Add column if does not exists
提问by user2165857
I'm new to using pandas and am writing a script where I read in a dataframe and then do some computation on some of the columns.
我是使用 Pandas 的新手，正在编写一个脚本，在其中读取数据帧，然后对某些列进行一些计算。
Sometimes I will have the column called "Met":
有时我会有一个名为“Met”的专栏：
df = pd.read_csv(File, sep='\t', compression='gzip', header=0, names=["Chrom", "Site", "coverage", "Met"])
Othertimes I will have:
其他时候我会有：
df = pd.read_csv(File, sep='\t', compression='gzip', header=0, names=["Chrom", "Site", "coverage", "freqC"])
I need to do some computation with the "Met" column so if it isn't present I will need to calculate it using:
我需要对“Met”列进行一些计算，因此如果它不存在，我将需要使用以下方法计算它：
df['Met'] = df['freqC'] * df['coverage']
is there a way to check if the "Met" column is present in the dataframe, and if not add it?
有没有办法检查数据框中是否存在“Met”列，如果没有，则添加它？
采纳答案by YS-L
You check it like this:
你这样检查：
if 'Met' not in df:
df['Met'] = df['freqC'] * df['coverage']
回答by autonopy
If you were creating the dataframe from scratch, you could create the missing columns without a loop merely by passing the column names into the pd.DataFrame()call:
如果您是从头开始创建数据框，则只需将列名传递到pd.DataFrame()调用中，就可以在没有循环的情况下创建缺失的列：
cols = ['column 1','column 2','column 3','column 4','column 5']
df = pd.DataFrame(list_or_dict, index=['a',], columns=cols)
