(require '[incanter.core :as icore])
;; Assume dataset "data" is already loaded by incanter.core/read-dataset
;; Let's examine the columns (note that Volume is the 5th column)
(icore/col-names data)
==> [:Date :Open :High :Low :Close :Volume]
;; We CAN use the :Volume keyword to look at just that column
(icore/sel data :cols Volume)
==> (11886469 9367474 12847099 9938230 11446219 12298336 15985045...)
;; But we CANNOT use the :Volume keyword with filters
;; (well, not without looking up the position in col-names first...)
(icore/sel data :filter #(> (#{:Volume} %) 1000000))
Obviously this is because the filter's anon function is looking at a LazySeq, which no longer has the column names as part of its structure, so the above code won't even compile. My question is this: Does Incanter have a way to perform this filtered query, still allowing me to use column keywords? For example, I can get this to work because I know that :Volume is the 5th column
(icore/sel data :filter #(> (nth % 5) 1000000))
Again, though, I'm looking to see if Incanter has a way of preserving the column keyword for this type of filtered query.
Example dataset:
(def data
(icore/dataset
[:foo :bar :baz :quux]
[[0 0 0 0]
[1 1 1 1]
[2 2 2 2]]))
Example query with result:
(icore/$where {:baz {:fn #(> % 1)}} data)
| :foo | :bar | :baz | :quux |
|------+------+------+-------|
| 2 | 2 | 2 | 2 |
Actually this could also be written
(icore/$where {:baz {:gt 1}} data)
Several such "predicate keywords" are support apart from :gt: :lt, :lte, :gte, :eq (corresponding to Clojure's =), :ne (not=), :in, :nin (not in).
:fn is the general "use any function" keyword.
All of these can be prefixed with $ (:$fn etc.) with no change in meaning.