I have a collection of files describing magazines content
<magazine>
<issue.number>22</issue.number>
<article>
<title>first article</title>
<subject>James</James>
</article>
<article>
<title>second article</title>
<subject>James</subject>
</article>
</magazine>
I want to output a list of articles in a format of <issue.number>, <title>.
So I created an XQuery:
for $x in /magazine
return concat($x/issue.number/text(),',',$x//title/text())
This results in an error, which I think is caused because the <issue.number> value is being returned twice. In eXist DB I get this:
The actual cardinality for parameter 1 does not match the cardinality declared in the function's signature: concat($atomizable-values as xdt:anyAtomicType?, ...) xs:string?. Expected cardinality: zero or one, got 2.
So if I can't use concat() what can I use?
The problem is that there are two articles in that magazine element, so you're passing two values as the third parameter of concat(...). Also, you don't need to use text() in here (and for most cases, shouldn't).
For once loop over the magazines, then again over the articles. It would be also fine to only loop over the articles, but then you'd have to use the parent-axis which I prefer to avoid.
for $magazine in $xml/magazine
for $article in $magazine/article
return concat($magazine/issue.number, ',', $article//title)
22,first article
22,second article
For concatenation over sequences of strings, have a look at string-join($sequence, $seperator). An example would be if you want all titles of one issue in a row.
for $magazine in $xml/magazine
return concat($magazine/issue.number, ': ', string-join($magazine//title, ', '))
which would return
22: first article, second article
Related
I am quite new to XQuery and I am trying to get a list of all elements and all attributes.
It should look like this:
element1 #attributex, #attribue y, ...
element 2 #attribute x, #attribute y, ...
element 3 #attribute x, #attribute y, ...
I am trying this so far, but the error "Item expected, sequence found":
for $x in collection("XYZ")
let $att := local-name(//#*)
let $ele := local-name(//*)
let $eleatt := string-join($ele, $att)
return $eleatt
I feel like I am turning an easy step into a complicated one. Please help.
Thanks in advance, Eleonore
//#* gives you a sequence of attribute nodes, //* a sequence of element nodes. In general to apply a function like local-name() to each item in a sequence, for nodes you have three options:
Use a final step /local-name() e.g. //#*/local-name() or //*/local-name()
In XQuery 3.1 use the map operator ! e.g. //#*!local-name()
Use a for .. return expression e.g. for $att in //#* return local-name($att)
The local-name() function takes a single node as its argument, not a sequence of nodes. To apply the same function to every node in a sequence, using the "!" operator: //*!local-name().
The string-join() function takes two arguments, a list of strings, and a separator. You're trying to pass two lists of strings. You want
string-join((//*!local-name(), //#*!local-name()), ',')
Of course you might also want to de-duplicate the list using distinct-values(), and to distinguish element from attribute names, or to associate attribute names with the element they appear on. That's all eminently possible. But for that, you'll have to ask a more precise question.
Like many, I'm tackling the Mondial database on XML. It would be a piece of cake, if XQuery syntax wasn't doing its best to sabotage.
let $inland := //province/#id
where every $sea in //sea satisfies
$sea/located/#province != $inland
return $inland
What I am trying to do in the above is find all "inland" provinces, the provinces that don't have a sea next to it. This, however, doesn't work, because the $sea/located/province is a big string, with every single province that it borders in it.
So I tried to modify into.
let $inland := //province/#id
where every $sea in //sea satisfies
not(contains($sea/located/#province, $inland))
return $inland
Where I would like it to only find the provinces that are a part of the sea's bordering provinces. Simple and straightforward.
Error message:
Stopped at C:/Users/saffekaffe/Desktop/mondial/xml/country_without_island.xml, 2/1:
[XPTY0004] Item expected, sequence found: (attribute id {"prov-Greece-2"},....
How do I get around this?
Example of //sea/located/province#
province="prov-France-5 prov-France-20 prov-France-89 prov-France-99"
Example of //province/#id
id="prov-Greece-2"
There are multiple ways in which XQuery works in a different way than you seem to expect.
The comparison operators = and != have existential semantics if at least one of their arguments is a sequence instead of a single item. This means that $seq1 = $seq2 is equivalent to some $x in $seq1, $y in $seq2 satisfies $x = $y. The query ('foo', 'bar') = ('bar', 'baz', 'quuz') returns true because there is at least one common item.
An XQuery exception like //province/#id evaluates to a sequence of all matching nodes. In your case that would be a sequence of over 1000 province IDs: (id="prov-cid-cia-Greece-2", id="prov-cid-cia-Greece-3", id="prov-cid-cia-Greece-4", [...]). This sequence is then bound to the variable $inland in your let clause. Since you don't iterate over individual items in $inland (for example using a for clause), the where condition then works on the whole sequence of all provinces worldwide at once. So your condition every $sea in //sea satisfies
$sea/located/#province != $inland now means:
"For every sea there is a province located next to it that has an #id that is not equal to at least one of all existing province IDs."
Th is returns false because there are seas with no located children, e.g.the Gulf of Aden.
contains($str, $sub) is not a good fit for checking if a substring is contained in a space-delimited string, because it also matches parts of entries: contains("foobar baz quux", "oob") returns true.
Instead you should either split the string into its parts using tokenize($str) and look through its parts, or use contains-token($str, $token).
Putting it all together, a correct query very similar to your original one is:
for $inland in //province/#id
where
every $sea in //sea
satisfies not(contains-token($sea/located/#province, $inland))
return $inland
Another approach would be to first gather all (unique) provinces that are next to seas and then return all provinces not in that sequence:
let $next-to-sea := distinct-values(//sea/located/#province/tokenize(.))
return //province/#id[not(. = $next-to-sea)]
Even more compact (but potentially less efficient):
//province/#id[not(. = //sea/located/#province/tokenize(.))]
On the other end of the spectrum you can use XQuery 3.0 maps to replace the potentially linear search through all seaside provinces by a single lookup:
let $seaside :=
map:merge(
for $id in //sea/located/#province/tokenize(.)
return map{ $id: () }
)
return //province/#id[not(map:contains($seaside, .))]
I have a MarkLogic 8 database in which there are documents which have two date time fields:
created-on
active-since
I am trying to write an Xquery to search all the documents for which the value of active-since is less than the value of created-on
Currently I am using the following FLWOR exression:
for $entity in fn:collection("entities")
let $id := fn:data($entity//id)
let $created-on := fn:data($entity//created-on)
let $active-since := fn:data($entity//active-since)
where $active-since < $created-on
return
(
$id,
$created-on,
$active-since
)
The above query takes too long to execute and with increase in the number of documents the execution time of this query will also increase.
Also, I have
element-range-index for both the above mentioned dateTime fields but they are not getting used here. The cts-element-query function only compares one element with a set of atomic values. In my case I am trying to compare two elements of the same document.
I think there should be a better and optimized solution for this problem.
Please let me know in case there is any search function or any other approach which will be suitable in this scenario.
This may be efficient enough for you.
Take one of the values and build a range query per value. This all uses the range indexes, so in that sense, it is efficient. However, at some point, there is a large query that us built. It reads similiar to a flword statement. If really wanted to be a bit more efficient, you could find out which if your elements had less unique values (size of the index) and use that for your iteration - thus building a smaller query. Also, you will note that on the element-values call, I also constrain it to your collection. This is just in case you happen to have that element in documents outside of your collection. This keeps the list to only those values you know are in your collection:
let $q := cts:or-query(
for $created-on in cts:element-values(xs:QName("created-on"), (), cts:collection-query("entities"))
return cts:element-value-range-query(xs:Qname("active-since"), "<" $created-on)
)
return
cts:search(
fn:collection("entities"),
$q
)
So, lets explain what is happening in a simple example:
Lets say I have elements A and B - each with a range index defined.
Lets pretend we have the combinations like this in 5 documents:
A,B
2,3
4,2
2,7
5,4
2,9
let $ := cts:or-query(
for $a in cts:element-values(xs:QName("A"))
return cts:element-value-range-query(xs:Qname("B"), "<" $a)
)
This would create the following query:
cts:or-query(
(
cts:element-value-range-query(xs:Qname("B"), "<" 2),
cts:element-value-range-query(xs:Qname("B"), "<" 4),
cts:element-value-range-query(xs:Qname("B"), "<" 5)
)
)
And in the example above, the only match would be the document with the combination: (5,4)
You might try using cts:tuple-values(). Pass in three references: active-since, created-on, and the URI reference. Then iterate the results looking for ones where active-since is less than created-on, and you'll have the URI of the doc.
It's not the prettiest code, but it will let all the data come from RAM, so it should scale nicely.
I am now using the following script to get the count of documents for which the value of active-since is less than the value of created-on:
fn:sum(
for $value-pairs in cts:value-tuples(
(
cts:element-reference(xs:QName("created-on")),
cts:element-reference(xs:QName("active-since"))
),
("fragment-frequency"),
cts:collection-query("entities")
)
let $created-on := json:array-values($value-pairs)[1]
let $active-since := json:array-values($value-pairs)[2]
return
if($active-since lt $created-on) then cts:frequency($value-pairs) else 0
)
Sorry for not having enough reputation, hence I need to comment here on your answer. Why do you think that ML will not return (2,3) and (4,2). I believe we are using an Or-query which will take any single query as true and return the document.
I am using IDL 8.4. I want to use isa() function to determine input type read by read_csv(). I want to use /number, /integer, /float and /string as some field I want to make sure float, other to be integer and other I don't care. I can do like this, but it is not very readable to human eye.
str = read_csv(filename, header=inheader)
; TODO check header
if not isa(str.(0), /integer) then stop
if not isa(str.(1), /number) then stop
if not isa(str.(2), /float) then stop
I am hoping I can do something like
expected_header = ['id', 'x', 'val']
expected_type = ['/integer', '/number', '/float']
str = read_csv(filename, header=inheader)
if not array_equal(strlowcase(inheader), expected_header) then stop
for i=0l,n_elements(expected_type) do
if not isa(str.(i), expected_type[i]) then stop
endfor
the above doesn't work, as '/integer' is taken literally and I guess isa() is looking for named structure. How can you do something similar?
Ideally I want to pick expected type based on header read from file, so that script still works as long as header specifies expected field.
EDIT:
my tentative solution is to write a wrapper for ISA(). Not very pretty, but does what I wanted... if there is cleaner solution , please let me know.
Also, read_csv is defined to return only one of long, long64, double and string, so I could write function to test with this limitation. but I just wanted to make it to work in general so that I can reuse them for other similar cases.
function isa_generic,var,typ
; calls isa() http://www.exelisvis.com/docs/ISA.html with keyword
; if 'n', test /number
; if 'i', test /integer
; if 'f', test /float
; if 's', test /string
if typ eq 'n' then return, isa(var, /number)
if typ eq 'i' then then return, isa(var, /integer)
if typ eq 'f' then then return, isa(var, /float)
if typ eq 's' then then return, isa(var, /string)
print, 'unexpected typename: ', typ
stop
end
IDL has some limited reflection abilities, which will do exactly what you want:
expected_types = ['integer', 'number', 'float']
expected_header = ['id', 'x', 'val']
str = read_csv(filename, header=inheader)
if ~array_equal(strlowcase(inheader), expected_header) then stop
foreach type, expected_types, index do begin
if ~isa(str.(index), _extra=create_struct(type, 1)) then stop
endforeach
It's debatable if this is really "easier to read" in your case, since there are only three cases to test. If there were 500 cases, it would be a lot cleaner than writing 500 slightly different lines.
This snipped used some rather esoteric IDL features, so let me explain what's happening a bit:
expected_types is just a list of (string) keyword names in the order they should be used.
The foreach part iterates over expected_types, putting the keyword string into the type variable and the iteration count into index.
This is equivalent to using for index = 0, n_elements(expected_types) - 1 do and then using expected_types[index] instead of type, but the foreach loop is easier to read IMHO. Reference here.
_extra is a special keyword that can pass a structure as if it were a set of keywords. Each of the structure's tags is interpreted as a keyword. Reference here.
The create_struct function takes one or more pairs of (string) tag names and (any type) values, then returns a structure with those tag names and values. Reference here.
Finally, I replaced not (bitwise not) with ~ (logical not). This step, like foreach vs for, is not necessary in this instance, but can avoid headache when debugging some types of code, where the distinction matters.
--
Reflective abilities like these can do an awful lot, and come in super handy. They're work-horses in other languages, but IDL programmers don't seem to use them as much. Here's a quick list of common reflective features I use in IDL, with links to the documentation for each:
create_struct - Create a structure from (string) tag names and values.
n_tags - Get the number of tags in a structure.
_extra, _strict_extra, and _ref_extra - Pass keywords by structure or reference.
call_function - Call a function by its (string) name.
call_procedure - Call a procedure by its (string) name.
call_method - Call a method (of an object) by its (string) name.
execute - Run complete IDL commands stored in a string.
Note: Be very careful using the execute function. It will blindly execute any IDL statement you (or a user, file, web form, etc.) feed it. Never ever feed untrusted or web user input to the IDL execute function.
You can't access the keywords quite like that, but there is a typename parameter to ISA that might be useful. This is untested, but should work:
expected_header = ['id', 'x', 'val']
expected_type = ['int', 'long', 'float']
str = read_cv(filename, header=inheader)
if not array_equal(strlowcase(inheader), expected_header) then stop
for i = 0L, n_elemented(expected_type) - 1L do begin
if not isa(str.(i), expected_type[i]) then stop
endfor
I'm looking to get all values associated with a key in a dictionary. Sometimes the key holds a single dictionary, sometimes a list of dictionaries.
a = {
'shelf':{
'book':{'title':'the catcher in the rye', 'author':'j d salinger'}
}
}
b = {
'shelf':[
{'book':{'title':'kafka on the shore', 'author':'haruki murakami'}},
{'book':{'title':'atomised', 'author':'michel houellebecq'}}
]
}
Here's my method to read the titles of every book on the shelf.
def print_books(d):
if(len(d['shelf']) == 1):
print d['shelf']['book']['title']
else:
for book in d['shelf']:
print book['book']['title']
It works, but doesn't look neat or pythonic. The for loop fails on the single value case, hence the if/else.
Can you improve on this?
Given your code will break if you have a list with a single item (and this is how I think it should be), if you really can't change your data structure this is a bit more robust and logic:
def print_books(d):
if isinstance(d['shelf'], dict):
print d['shelf']['book']['title']
else:
for book in d['shelf']:
print book['book']['title']
Why not always make 'shelf' map to a list of elements, but in the single element case it's a ... single element list? Then you'd always be able to treat each bookshelf the same.
def print_books(d):
container = d['shelf']
books = container if isinstance(container, list) else [container['book']]
books = [ e['book'] for e in books ]
for book in books:
print book['title']
I would first get the input consistent, then loop through all the books even if only one.
def print_books(d):
books = d['shelf'] if type(d['shelf']) is list else [ d['shelf'] ]
for book in books:
print book['book']['title']
I think this looks a little neater and pythonic, although some might argue not as efficient as your original code to create an array with one element and loop through it.