[R] need help with unlist(), losing NULL values

[dinesh]

Hi,

I have a very rudimentary kind of question on using unlist(). I am 
parsing a bunch of JSON text using rjson package. Some data elements in 
a dictionary happen to be null which rjson parses correctly.

 > fromJSON(json_str='{"query":{"A":10, "B":null, "C":"hello"}, 
"query":{"A":20, "B":null, "C":"hello again"}}')
$query
$query$A
[1] 10

$query$B
NULL

$query$C
[1] "hello"


$query
$query$A
[1] 20

$query$B
NULL

$query$C
[1] "hello again"


I need to view this as a matrix, for example as
matrix(unlist(fromJSON(json_str='{"query":{"A":10, "B":null, 
"C":"hello"}, "query":{"A":20, "B":null, "C":"hello again"}}')), nr=2)
BUT I lose column "B". It gets worse if some of the B's are not null, 
and if I were really unlucky then matrix() would not fail but data will 
be messed up.

My question is - is there a different way of using unlist() that I am 
missing? Is there a better way of getting this data in a rectangular format?

-- 
Thanks and regards,
Dinesh