Check if a value is present in each group

[Menthix]

Haha, what a wonderful thing the Internet is: instant answers

I could never have got to this on my own!

df['Result'] = df['Type'].isin(df.loc[df['Var1'].eq(3), 'Type']).astype(int)
df['Result'] = np.where(df['Type'].isin(df.loc[df['Var1'].eq(3), 'Type']), 1, 0)
df['Result'] = df['Var1'].eq(3).groupby(df['Type']).transform('any').astype(int)

Thank you so much, it works !! :D