Python Pandas DataFrame从列中选择行

Question

In an Excel sheet with columns Rainfall / Year / Month, I want to sum rainfall data per year. That is, for instance, for the year 2000, from month 1 to 12, summing all the Rainfall cells into a new one. I tried using pandas in Python but cannot manage (just started coding). How can I proceed? Any help is welcome, thanks!

Here the head of the data (which has been downloaded):

   rainfall (mm)  \tyear   month  country   iso3   iso2
0      120.54000    1990       1      ECU    NaN    NaN
1      231.15652    1990       2      ECU    NaN    NaN
2      136.62088    1990       3      ECU    NaN    NaN
3      203.47653    1990       4      ECU    NaN    NaN
4      164.20956    1990       5      ECU    NaN    NaN

Answer 1

Use groupby and aggregate sum if need sum of all years:

df = df.groupby('\tyear')['rainfall (mm)'].sum()

But if need only one value:

df.loc[df['\tyear'] == 2000, 'rainfall (mm)'].sum()

Answer 2

If you just want the year 2000, use

df[df['\tyear'] == 2000]['rainfall (mm)'].sum()

Otherwise, jezrael's answer is nice because it sums rainfall (mm) for each distinct value of \\tyear .