Parsing JSON from Google Distance Matrix API with Corona SDK - json

Question

So I'm trying to pull data from a JSON string (as seen below). When I decode the JSON using the code below, and then attempt to index the duration text, I get a nil return. I have tried everything and nothing seems to work.
Here is the Google Distance Matrix API JSON:
{
"destination_addresses" : [ "San Francisco, CA, USA" ],
"origin_addresses" : [ "Seattle, WA, USA" ],
"rows" : [
{
"elements" : [
{
"distance" : {
"text" : "1,299 km",
"value" : 1299026
},
"duration" : {
"text" : "12 hours 18 mins",
"value" : 44303
},
"status" : "OK"
}]
}],
"status" : "OK"
}
And here is my code:
local json = require ("json")
local http = require("socket.http")
local myNewData1 = {}
local SaveData1 = function (event)
distanceReturn = ""
distance = ""
local URL1 = "http://maps.googleapis.com/maps/api/distancematrix/json?origins=Seattle&destinations=San+Francisco&mode=driving&&sensor=false"
local response1 = http.request(URL1)
local data2 = json.decode(response1)
if response1 == nil then
native.showAlert( "Data is nill", { "OK"})
print("Error1")
distanceReturn = "Error1"
elseif data2 == nill then
distanceReturn = "Error2"
native.showAlert( "Data is nill", { "OK"})
print("Error2")
else
for i = 1, #data2 do
print("Working")
print(data2[i].rows)
for j = 1, #data2[i].rows, 1 do
print("\t" .. data2[i].rows[j])
for k = 1, #data2[i].rows[k].elements, 1 do
print("\t" .. data2[i].rows[j].elements[k])
for g = 1, #data2[i].rows[k].elements[k].duration, 1 do
print("\t" .. data2[i].rows[k].elements[k].duration[g])
for f = 1, #data2[i].rows[k].elements[k].duration[g].text, 1 do
print("\t" .. data2[i].rows[k].elements[k].duration[g].text)
distance = data2[i].rows[k].elements[k].duration[g].text
distanceReturn = data2[i].rows[k].elements[k].duration[g].text
end
end
end
end
end
end
timer.performWithDelay (100, SaveData1, 999999)

Answer 1

Your loops are not correct. Try this shorter solution.
Replace all your "for i = 1, #data2 do" loop for this one below:
print("Working")
for i,row in ipairs(data2.rows) do
for j,element in ipairs(row.elements) do
print(element.duration.text)
end
end

Answer 2

This question was solved on Corona Forums by Rob Miracle (http://forums.coronalabs.com/topic/47319-parsing-json-from-google-distance-matrix-api/?hl=print_r#entry244400). The solution is simple:
"JSON and Lua tables are almost identical data structures. In this case your table data2 has top level entries:
data2.destination_addresses
data2.origin_addresses
data2.rows
data2.status
Now data2.rows is another table that is indexed by numbers (the [] brackets) but here is only one of them, but its still an array entry:
data.rows[1]
Then inside of it is another numerically indexed table called elements.
So far to get to the element they are (again there is only one of them
data2.rows[1].elements[1]
then it's just accessing the remaining elements:
data2.rows[1].elements[1].distance.text
data2.rows[1].elements[1].distance.value
data2.rows[1].elements[1].duration.text
data2.rows[1].elements[1].duration.value
There is a great table printing function called print_r which can be found in the community code which is great for dumping tables like this to see their structure."