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### sum
```
number sum(array[number] value)
```
Returns the sum of the items in an array of numbers.
Returns 0 if the array is empty.
It is a type error if any item in the array is not a number.
### Examples
```cpp
#include <iostream>
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpath/jsonpath.hpp>
// for brevity
using jsoncons::json;
namespace jsonpath = jsoncons::jsonpath;
int main()
{
std::string data = R"(
{
"books":
[
{
"title" : "A Wild Sheep Chase",
"author" : "Haruki Murakami",
"price" : 22.72
},
{
"title" : "The Night Watch",
"author" : "Sergei Lukyanenko",
"price" : 23.58
},
{
"title" : "The Comedians",
"author" : "Graham Greene",
"price" : 21.99
},
{
"title" : "The Night Watch",
"author" : "Phillips, David Atlee"
}
]
}
)";
json j = json::parse(data);
// All titles whose price is greater than the average price
std::string expr = R"($.books[?(@.price > sum($.books[*].price)/length($.books[*].price))].title)";
json result = jsonpath::json_query(j, expr);
std::cout << result << "\n\n";
}
```
Output:
```
["The Night Watch"]
```
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