I have a list of objects that are returned as a sequence, I would like to retrieve the keys of each object so as to be able to display the object correctly. At the moment I try data?first?keys which seems to get something like the queries that return the objects (Not sure how to explain that last sentence either but img below shows what I'm trying to explain).
The objects amount of objects returned are correct (7) but displaying the keys for each object is my aim. The macro that attempts this is here (from the apache ofbiz development book chapter 8).
Seems like it my sequence is a list of hashes and as explained by Daniel Dekany this post:
The original problem is that, someHash[key] expects a
string as key. Because, the hash type of FTL, by definition, maps
string keys to arbitrary values. It's not the same as Java's Map.
(Note that to further complicate the matters, in FTL
someSequenceOrString[index] expects an integer index. So, the [] thing
is used for that too.) Now someBeanWrappedMap(key) has technically
nothing to do with all the []-s, it's just a method call, so it
accepts all kind of keys. If you have a Map with non-string keys, you
must use that.
Thanks D Dekany if you're on stack, this ended my half day frustration with the ftl template.
Related
My question is theoretical,
I'm trying to make a design for a mapreduce example in Big data processing.
The case which I have requires a pair of keys to be mapped to a pair of values.
for example if we have below text:
"Bachelors in Engineering has experience of 5 years"
I am trying to count the words Engineering & Experience in a way where I would have a value for each word separately.
So my key would be (Engineering,Experience) and my value would be (1,1) as per the above given text example.
Note that there is a relationship between both key values in my homework, therefore I want them both in one set of a key-value to determine if both keys are mentioned in one text file, or only one key is mentioned, or none is mentioned.
Please let me know if above case is possible to do in map-reduce of big data or not..
Having a string key of "(Engineering,Experience)" is no different than just having a String of one of those words.
If you want to have some more custom type, then you will want to subclass the Writable and maybe the WritableComparable interfaces.
Simlarly, for the value, you could put the entire tuple as Text and parse it later, or you can create your own Writable subclass that can store two integers.
Thanks for the Answer, but I figured I could use "Engineering Experience" as a string for the key.
Is it possible to compare the function of an existing index with an ordinary native function in JavaScript?
For instance, I might create an index with the following code:
r.table('Table').indexCreate('index', document => document.hasFields('field'));
I might then, later, wish to determine whether the index has the same function:
document => document.hasFields('field')
Using indexStatus(), two properties may be able to help with this.
First, function is a Buffer representing the function, and can be compared with Buffers obtained from other indexStatus() objects. However, it's not clear how this could be compared with a native JavaScript function. A new index could be created, and then its Buffer compared with the Buffer of the existing index, but this would be a messy and performance-impacting workaround.
Second, query is a string containing a function resembling that which was provided to indexCreate(). However, this property seems to be undocumented, and the value is not always exactly the same as the function provided to indexCreate(), with changes to variable names and the transformation of arrow functions to function expressions. I've written some rough code which tries to work with this approach, although it's imperfect, given the opaque nature of the rules by which the query value is generated by RethinkDB.
I used to have a series of independent arrays (e.g. name(), id(), description() ). I used to be able to check whether a value existed in a specific array by doing name.include?("Mark")
Now that I moved to a MUCH MORE elegant way to manage different these independent arrays (here for background: How do I convert an Array with a JSON string into a JSON object (ruby)) I am trying to figure out how I do the same.
In short I put all the independent arrays in a single structure so that I can reference the content as object().name, object().id, object().description.
However I am missing now how I can check whether the object array has a value "Mark" in its name structure.
I have tried object.name.include?("Mark") but it doesn't quite like it.
I have also tried to use has_value?but that doesn't seem to be working either (likely because it used to be an hash before I imported it into the structure but right now is no longer a hash - see here: How do I convert an Array with a JSON string into a JSON object (ruby))
Thoughts? How can I check whether object.name contains a certain string?
Thanks.
If you want to find all customers called Mark you can write the following:
customers_named_mark = array_of_customers.select{|c| c.name == 'Mark' }
This will return a potentially empty array.
If you want to find the first customer named Mark, write
customer_named_mark = array_of_customers.detect{|c| c.name == 'Mark' }
This will return the first matching item or nil.
For example, key 1 will have values "A","B","C" but key 2 will have value "D". If I use
Map<String, List<String>>
I need to populate the List<String> even when I have only single String value.
What data structure should be used in this case?
Map<String,List<String>> would be the standard way to do it (using a size-1 list when there is only a single item).
You could also have something like Map<String, Object> (which should work in either Java or presumably C#, to name two), where the value is either List<String> or String, but this would be fairly bad practice, as there are readability issue (you don't know what Object represents right off the bat from seeing the type), casting happens during runtime, which isn't ideal, among other things.
It does however depend what type of queries you plan to run. Map<String,Set<String>> might be a good idea if you plan of doing existence checks in the List and it can be large. Set<StringPair> (where StringPair is a class with 2 String members) is another consideration if there are plenty of keys with only 1 mapped value. There are plenty of solutions which would be more appropriate under various circumstances - it basically comes down to looking at the type of queries you want to perform and picking an appropriate structure according to that.
I have a couchdb view set up using an array key value, in the format:
[articleId, -timestamp]
I want to query for all entries with the same article id. All timestamps are acceptable.
Right now I am using a query like this:
?startkey=["A697CA3027682D5JSSC",-9999999999999]&endkey=["A697CA3027682D5JSSC",0]
but I would like something a bit simpler.
Is there an easy way to completely wildcard the second key element? What would be the simplest syntax for this?
First, as a comment pointed out, there is indeed a special value {} that is ordered after any value, so your query becomes:
startkey=["target ID"]&endkey=["target ID",{}]
This is as equivalent to a wildcard match.
As a side note, there is no need to reverse the ordering in the map function by emitting a negative timestamp, you can reverse the order as an option to the view invocation (your start and end key will be swapped).
startkey=["target ID",{}]&endkey=["target ID"]&descending=true
For future reference, in CouchDB 3 you can use "\ufff0" instead of {}, which would be ordered after a string or number, but before an object.
From the CouchDB 3 docs:
Beware that {} is no longer a suitable “high” key sentinel value. Use a string like "\ufff0" instead.
The query startkey=["foo"]&endkey=["foo",{}] will match most array keys with “foo” in the first element, such as ["foo","bar"] and ["foo",["bar","baz"]]. However it will not match ["foo",{"an":"object"}]