Is it possible to perform std.algorithm.reduce with the seed being an array of strings? Something like this:
reduce!(string[], (r,c) => r ~= c)([], someIterable);
Sure, but due to the nature of dynamic arrays you have to declare it first:
string[] arr;
reduce!((r, c) => r~=c)(arr, someIterable);
Related
I want to use the MarkLogic optic API to join two range indexes but somehow they don't join. Is the query I wrote wrong or can't I compare the indexes used?
I have two indexes defined:
an element-attribute range index x/#refid
a range field index 'id'
Both are of type string and have the same collation defined. Both indexes have data that I can retrieve with cts:values() function. Both are huge indexes and I want to join them using optics so I have constructed the following query :
import module namespace op="http://marklogic.com/optic"
at "/MarkLogic/optic.xqy";
let $subfrag := op:fragment-id-col("subfrag")
let $notfrag := op:fragment-id-col("notfrag")
let $query :=
cts:and-query((
cts:collection-query("latest")
))
let $subids := op:from-lexicons(
map:entry("subid", cts:field-reference("id")), (), $subfrag) => op:where($query)
let $notids := op:from-lexicons(
map:entry("notid", cts:element-attribute-reference(xs:QName("x"), xs:QName("refid"))),
(),
$notfrag)
return $subids
=> op:join-cross-product($notids)
=> op:where(op:eq($notfrag, $subfrag))
=> op:result()
This query uses the join-cross-product and when I remove the op:where clause I get all values left and right. I verified and some are equal so the clause should filter only those rows i'm actually interested in. But somehow it doesn't work and I get an empty result. Also, if I replace one of the values in the op:eq with a string value it doesn't return a result.
When I use the same variable in the op:eq operator (like op:eq($notfrag, $notfrag)) I get results back so the statement as is works. Just not the comparison between the two indexes.
I have also used variants with join-inner and left-outer-join but those are also returning no results.
Am I comparing two incomparable indexes or am I missing some statement (as documentation/example is a bit thin).
(of course I can solve by not using optics but in this case it would be a perfect fit)
[update]
I got it working by eventually by changing the final statement:
return $subids
=> op:join-cross-product($notids)
=> op:where(op:eq(op:col('subid'), op:col('notid')))
=> op:result()
So somehow you cannot use the fragment definitions in the condition. After this I replaced the join-cross-product with a join-inner construction which should be a bit more efficient.
And to be complete, I initially used the example from the MarkLogic documentation found here (https://docs.marklogic.com/guide/app-dev/OpticAPI#id_87356), specifically the last example where they use a fragment column definition to be used as param in the join-inner statement that didn't work in my case.
Cross products are typically useful only for small rows sets.
Putting both reference in the same from-lexicons() accessor does an implicit join, meaning that the engine forms rows by constructing a local cross-product of the values indexed for each document.
Such a query could be expressed by:
op:from-lexicons(
map:entry("subid", cts:field-reference("id"))
=>map:with("notid", cts:element-attribute-reference(xs:QName("x"),
xs:QName("refid")))
=>op:where(cts:collection-query("latest"))
=>op:result()
Making the joins explicitly could be done with:
let $subids := op:from-lexicons(
map:entry("subid", cts:field-reference("id")), (), $subfrag)
=> op:where($query)
let $notids := op:from-lexicons(
map:entry("notid", cts:element-attribute-reference(xs:QName("x"),
xs:QName("refid"))),
(),
$notfrag)
return $subids
=> op:join-inner($notids, op:on($notfrag, $subfrag))
=> op:result()
Hoping that helps,
I wanted to make a function that looks at every column of a DataFrame and return a boolean, so I end up with an array of booleans. Here is the code
# some random dataframe
df = DataFrame([1:3, 4:6])
# a function that returns an array of boolean
function some_bool_fn(df)::Array{Bool}
array_of_arrays = colwise(df) do sdd3
# for illustration only
return true
end
array = [a[1] for a in array_of_arrays]
return array
end
# calling the function
some_bool_fn(dd3)
This works except I find the line
array = [a[1] for a in array_of_arrays]
a bit wasteful. Basically I get an array of arrays as the output of colwise, so I then had to put the array of arrays into a simple array of bools. Is there a way to write the code so I can avoid this line of code?
As #Gnimuc commented this behaviour is changing.
If you look at master branch: https://github.com/JuliaData/DataFrames.jl/blob/master/src/groupeddataframe/grouping.jl#L241 you'll see another version. You could probably copy it:
mycolwise(f, d::AbstractDataFrame) = [f(d[i]) for i in 1:ncol(d)]
Suppose I have a certain value, and I want to do something with it depending on certain characteristics it might have.
For example, suppose the value is a string, and I want to print it to the screen if it starts with the letter L, save it to a file if it's length is less than 20 characters, and play a sound if the last character is the same as the first one.
One option of course is a simple if else if construct:
if (value[0] == 'L')
....
else if (value.Length < 20)
....
else if (value[0] == value.Last())
....
However with a lot of conditions, this can get ugly really fast. So the other option is a Dictionary. However I'm not sure how I can use a Dictionary to achieve this.
How can this be done?
You can construct a dictionary that contains conditions and actions that should be performed if a condition is met. In general, if you need to work with type T, this dictionary will have a type Dictionary<Predicate<T>, Action<T>>. For a string it can be:
var conditions = new Dictionary<Predicate<string>, Action<string>>
{
{s => s.StartsWith("L"), s => Console.WriteLine("Starts with L")},
{s => s.Length < 20, s => Console.WriteLine("Has fewer that 20 symbols")},
};
string input = "some input";
foreach (var condition in conditions)
{
if (condition.Key(input)) condition.Value(input);
}
In fact, you don't even need a Dictionary here - you can use List<Tuple<Predicate<string>, Action<string>>>, or, even better - to introduce a simple small class that contains a predicate and an action.
I am trying to store contents of different vectors in a matrix.
length of vectors are different and they are all strings. lets say:
A=["MXAA', "MXBB", "MXCC"]
B=["JJJ", "LKLKLKL"]
so the new matrix should look like the following:
C= [MXAA, MXBB, MXCC;JJJ, LKLKLKL, 0]
is the a way to do that in C?
thanks
You would need to create an array of pointers to pointer to the element type (which in your case is a pointer to char).
The problem you need to consider is that every array is different size; so I suggest you store the size of the arrays, or you will quickly end up running over the bounds of an array. This sounds a bit like a custom type.
typedef {
int n;
char **strArr;
} stringArray;
stringArray *str2d;
str2d = (stringArray*) malloc(2*sizeof(stringArray));
str2d[0].n=3;
str2d[0].strArr = (char**)malloc(3*sizeof(char*));
str2d[0].strArr[0] = "MXAA";
str2d[0].strArr[1] = "MXBB";
str2d[0].strArr[2] = "MXCC";
str2d[1].n = 2;
str2d[1].strArr = (char**)malloc(2*sizeof(char*));
str2d[1].strArr[0] = "JJJ";
str2d[1].strArr[1] = "LKLKLKL";
If you want to access an element you use similar addressing - but check that you stay within bounds!
I deliberately did this in very explicit steps, hoping this makes the principle clear. There are better ways to do this but they are more obscure (or not "standard C")
So instead of writing a looping function where you instantiate an array and then set each index value as the index, is there a way to do this in LINQ?
Enumerable.Range(0, 10) will give you an IEnumerable<int> containing zero to 9.
You can use the System.Linq.Enumerable.Range method for this purpose.
Generates a sequence of integral numbers within a specified range.
For example:
var zeroToNineArray = Enumerable.Range(0, 10).ToArray();
will create an array of sequential integers with values in the inclusive range [0, 9].
You might want to look at Enumberable.Range
For Each( var i in Enumberable.Range(1,5).ToArray()){
Console.WriteLine(i)
}
would print out 1,2,3,4,5