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Automatic ordered JSON #424
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https://github.com/nlohmann/json/blob/master/.github/CONTRIBUTING.md
We do not preserve the insertion order of object elements. The JSON standard defines objects as "an unordered collection of zero or more name/value pairs". To this end, this library does not preserve insertion order of name/value pairs. (In fact, keys will be traversed in alphabetical order as std::map with std::less is used by default.) Note this behavior conforms to the standard, and we shall not it to any other order.
You can check out https://github.com/nlohmann/fifo_map - it should work as a replacement of std::map and maintains the key's order.
Reacted by Mickaël Bettinelli and menkaurHi. A quick question regarding this issue (just out of curious): why not use std::unordered_map by default instead of std::map? After all, json objects are unsorted by semantics. And unordered_map should gain significant speed up regarding the time complexity.
Reacted by menkaurThe problem is that we are defining an object
basic_jsonand inside a member of typestd::map<std::string, basic_json>. At this point,basic_jsonis not yet fully defined. This seems to be OK forstd::mapon all platforms/compilers I encountered so far, but it is not forstd::unordered_map.Hi, is there any way to sort nlohmann::json depending upon values, like for example,
if key is string and value is double, can I sort json based on double?Can you give an example for this?
Example:
if input = {
"abc" : 0.288,
"pqr" : 0.176,
"xyz" : 0.555,
"zaz" : 0.345
}
After sorting it should look something like,
output = {
"pqr" : 0.176,
"abc" : 0.288,
"lmo" : 0.345,
"xyz" : 0.555
}
Basically sorted by values.This is not possible in the library (see https://github.com/nlohmann/json#order-of-object-keys). You could parse the value into some C++ container (e.g., a vector of pairs) and sort it yourself.
Thanks for the support.
Hey, is there a way to use std::max_element with nlohmann::json to get the key-value pair with the highest value for the above-given example?
prototype:
auto max = std::max_element (j.begin(), j.end(), cmp);You may be able to achieve this via the
items()function.
Hi,
Json is automatically sorted by an alphabetic order. I don't find any information about that in your readme. Is there a way to avoid sorting ?