parsing out value from multi value field

[dtakacssplunk]

I have data in the following form:

field A,    field B(this is an array)

a              {"k":1}

                {"k":2}

                {"k":3}

b              {"k":1}

                {"k":1}

                {"k":1}

field B is an array, I want to produce table like this

field A, sumB

a     6

b    3

what is the way to extract the values and add them up?

my thinking was to do 

| eval value=spath(fieldB, "k") 

and I was expecting values to have array 1,2,3 and 1,1,1 but they did not

[thambisetty]

| rex field=fieldB "k\":(?<fieldb_val>\d+)"

| stats sum(fieldb_val) by fieldA