What's the best way to store the following message into a data structure for easy access?

"A=abc,B=156,F=3,G=1,H=10,G=2,H=20,G=3,H=30,X=23.50,Y=xyz"

The above consists of key/value pairs of the following:

A=abc  

B=156  

F=3  

G=1  

H=10  

G=2  

H=20  

G=3  

H=30  

X=23.50  

Y=xyz  

The tricky part is the keys F, G and H. F indicates the number of items in a group whose item consists of G and H.

For example if F=3, there are three items in this group:
Item 1: G=1, H=10
Item 2: G=2, H=20
Item 3: G=3, H=30

In the above example, each item consists of two key/pair values: G and H. I would like the data structure to be flexible such that it can handle if the item increases its key/pair values. As much as possible, I would like to maintain the order it appears in the string.

UPDATE: I would like to store the key/value pairs as strings even though the value often appears as float or other data type, like a map.