I have three columns: id(unique), value, time

I want to create a new column that does a simple row_number without any partitioning

I tried : df['test'] = df.groupby('id_col').cumcount() 1

But the output is only ones.

Expecting to get 1->len of the dataframe

Also , is there a way to do it in numpy for better performance

CodePudding user response：

If your index is already ordered starting from 0

df["row_num"] = df.index   1

else:

df["row_num"] = df.reset_index().index   1

Comparing time with %%timeit speed from fastest to slowest: @Scott Boston's method > @Henry Ecker's method > mine

CodePudding user response：

df["row_num"] = range(1,len(df) 1)

Alternative:

df.insert(0, "row_num", range(1,len(df) 1))