Extracting json data from an OData API gives inconsistent results?

[maja]

I'm attempting to extract data from the Wales government statistics services OData API. Details on the API can be found here, including an example of how to filter the data.

However I seem to be getting a non-deterministic subset of the data i.e. each attempt results in a different number of records returned.

Below is a simple reproducible example.

Additionally I have also tried (HT @martinjhnhadley):

• using RJSONIO::fromJSON(), which has the same result.
• attempting to use the odata.nextLink url, if it is returned in the json object, to keep extracting more data. Again, each attempt results in a different sized object.

Any insight will be much appreciated!

## preliminaries
library(jsonlite)

# prepare filters
filter1 <- "Column_ItemName_ENG"
filter1.value <- "Gross%20expenditure"
filter2 <- "Row_ItemName_ENG"
filter2.value <- "Parking%20of%20vehicles"

query <- paste0("http://open.statswales.gov.wales/en-gb/dataset/lgfs0009?$filter=",
                filter1, "%20eq%20%27", filter1.value, "%27%20and%20",
                filter2, "%20eq%20%27", filter2.value, "%27")

# test 1
test1 <- jsonlite::fromJSON(query)
test1 <- test1[[2]]

# test 2
test2 <- jsonlite::fromJSON(query)
test2 <- test2[[2]]

# test 3
test3 <- jsonlite::fromJSON(query)
test3 <- test3[[2]]

# compare results
nrow(test1)
nrow(test2)
nrow(test3)

PS: I have cross-posted this question to Stackoverflow, and I promise to update either post with relevant solutions found on the other one.