Fixed JSON infer order

Cargo.toml

@@ -47,7 +47,7 @@ regex-syntax = { version = "^0.6", optional = true }
 streaming-iterator = { version = "0.1", optional = true }
 fallible-streaming-iterator = { version = "0.1", optional = true }
 
-json-deserializer = { version = "0.3", optional = true }
+json-deserializer = { version = "0.4", optional = true, features = ["preserve_order"] }
 indexmap = { version = "^1.6", optional = true }
 
 # used to print columns in a nice columnar format

src/io/json/read/infer_schema.rs

@@ -1,5 +1,4 @@
 use std::borrow::Borrow;
-use std::collections::BTreeMap;
 
 use indexmap::map::IndexMap as HashMap;
 use indexmap::set::IndexSet as HashSet;
@@ -30,7 +29,7 @@ fn filter_map_nulls(dt: DataType) -> Option<DataType> {
     }
 }
 
-fn infer_object(inner: &BTreeMap<String, Value>) -> Result<DataType> {
+fn infer_object(inner: &HashMap<String, Value>) -> Result<DataType> {
     let fields = inner
         .iter()
         .filter_map(|(key, value)| {

tests/it/io/ndjson/mod.rs

@@ -311,3 +311,22 @@ fn case(case: &str) -> (String, Box<dyn Array>) {
         _ => todo!(),
     }
 }
+
+#[test]
+fn infer_object() -> Result<()> {
+    let data = r#"{"i64": 1, "f64": 0.1, "utf8": "foo1", "bools": true}
+    {"i64": 2, "f64": 0.2, "utf8": "foo2", "bools": false}
+    {"i64": 3, "f64": 0.3, "utf8": "foo3"}
+    {"i64": 4, "f64": 0.4, "utf8": "foo4", "bools": false}
+    "#;
+    let u64_fld = Field::new("i64", DataType::Int64, true);
+    let f64_fld = Field::new("f64", DataType::Float64, true);
+    let utf8_fld = Field::new("utf8", DataType::Utf8, true);
+    let bools_fld = Field::new("bools", DataType::Boolean, true);
+
+    let expected = DataType::Struct(vec![u64_fld, f64_fld, utf8_fld, bools_fld]);
+    let actual = infer(data)?;
+
+    assert_eq!(expected, actual);
+    Ok(())
+}