user 1    user 2     7
user 1    user 3     19
user 1    user 7     5
user 3    user 2     1
user 2    user 7     1

user 1 user 2 user 3  user 7
user 1
user 3
user 2
user 7

user 1 user 2 user 3  user 7
user 1        0        7     19       5
user 3        0        1      0       0
user 2        0        0      0       1
user 7        0        0      0       0

=SUMIFS(Sheet1!$C:$C,Sheet1!$A:$A,$A2,Sheet1!$B:$B,B$1)