Read first line of huge Json file with Spark using Pyspark - json

Question

I'm pretty new to Spark and to teach myself I have been using small json files, which work perfectly. I'm using Pyspark with Spark 2.2.1 However I don't get how to read in a single data line instead of the entire json file. I have been looking for documentation on this but it seems pretty scarce. I have to process a single large (larger than my RAM) json file (wikipedia dump: https://archive.org/details/wikidata-json-20150316) and want to do this in chuncks or line by line. I thought Spark was designed to do just that but can't find out how to do it and when I request the top 5 observations in a naive way I run out of memory. I have tried RDD .
SparkRDD= spark.read.json("largejson.json").rdd
SparkRDD.take(5)
and Dataframe
SparkDF= spark.read.json("largejson.json")
SparkDF.show(5,truncate = False)
So in short:
1) How do I read in just a fraction of a large JSON file? (Show first 5 entries)
2) How do I filter a large JSON file line by line to keep just the required results?
Also: I don't want to predefine the datascheme for this to work.
I must be overlooking something.
Thanks
Edit: With some help I have gotten a look at the first observation but it by itself is already too huge to post here so I'll just put a fraction of it here.
[
{
"id": "Q1",
"type": "item",
"aliases": {
"pl": [{
"language": "pl",
"value": "kosmos"
}, {
"language": "pl",
"value": "\\u015bwiat"
}, {
"language": "pl",
"value": "natura"
}, {
"language": "pl",
"value": "uniwersum"
}],
"en": [{
"language": "en",
"value": "cosmos"
}, {
"language": "en",
"value": "The Universe"
}, {
"language": "en",
"value": "Space"
}],
...etc

Answer 1

That's very similar to Select only first line from files under a directory in pyspark
Hence something like this should work :
def read_firstline(filename):
with open(filename, 'rb') as f:
return f.readline()
# files is a list of filenames
rdd_of_firstlines = sc.parallelize(files).flatMap(read_firstline)