Remove specific XML nodes using Clojure

Question

I have the following XML structure:

(def xmlstr
\"
  
    AAA         


        

Answer 1

The Tupelo library can easily solve this problem using tupelo.forest. You can find the API docs on GitHub Pages. Below is a test case using your example.

Here we load your xml data and convert it first into enlive and then the native tree structure used by tupelo.forest:

(ns tst.tupelo.forest-examples
  (:use tupelo.forest tupelo.test )
  (:require
    [clojure.data.xml :as dx]
    [clojure.java.io :as io]
    [clojure.set :as cs]
    [net.cgrand.enlive-html :as en-html]
    [schema.core :as s]
    [tupelo.core :as t]
    [tupelo.string :as ts]))
(t/refer-tupelo)

; Discard any xml nodes of Type="A" or Type="B" (plus blank string nodes)
(dotest
  (with-forest (new-forest)
    (let [xml-str         "
                            
                              AAA1
                              BBB1
                              CCC1
                              AAA2
                            
                          "
          enlive-tree     (->> xml-str
                            java.io.StringReader.
                            en-html/html-resource
                            first)
          root-hid        (add-tree-enlive enlive-tree)
          tree-1          (hid->tree root-hid)

The hid suffix stands for "Hex ID" which is unique hex value that acts like a pointer to a node/leaf in the tree. At this stage we have just loaded the data in the forest data structure, creating tree-1 which looks like:

 (is= tree-1
   {:attrs {:tag :ROOT},
    :kids  [{:attrs {:tag :tupelo.forest/raw},
             :value "\n                            "}
            {:attrs {:tag :Items},
             :kids  [{:attrs {:tag :tupelo.forest/raw},
                      :value "\n                              "}
                     {:attrs {:tag :Item},
                      :kids  [{:attrs {:tag :Type}, :value "A"}
                              {:attrs {:tag :Note}, :value "AA1"}]}
                     {:attrs {:tag :tupelo.forest/raw},
                      :value "\n                              "}
                     {:attrs {:tag :Item},
                      :kids  [{:attrs {:tag :Type}, :value "B"}
                              {:attrs {:tag :Note}, :value "BB1"}]}
                     {:attrs {:tag :tupelo.forest/raw},
                      :value "\n                              "}
                     {:attrs {:tag :Item},
                      :kids  [{:attrs {:tag :Type}, :value "C"}
                              {:attrs {:tag :Note}, :value "CC1"}]}
                     {:attrs {:tag :tupelo.forest/raw},
                      :value "\n                              "}
                     {:attrs {:tag :Item},
                      :kids  [{:attrs {:tag :Type}, :value "A"}
                              {:attrs {:tag :Note}, :value "AA2"}]}
                     {:attrs {:tag :tupelo.forest/raw},
                      :value "\n                            "}]}
            {:attrs {:tag :tupelo.forest/raw},
             :value "\n                          "}]})

We next remove any blank strings with this code:

blank-leaf-hid? (fn [hid] (and (leaf-hid? hid) ; ensure it is a leaf node
                            (let [value (hid->value hid)]
                              (and (string? value)
                                (or (zero? (count value)) ; empty string
                                  (ts/whitespace? value)))))) ; all whitespace string

blank-leaf-hids (keep-if blank-leaf-hid? (all-hids))
>>              (apply remove-hid blank-leaf-hids)
tree-2          (hid->tree root-hid)

yielding tree-2 which looks much neater:

(is= tree-2
  {:attrs {:tag :ROOT},
   :kids  [{:attrs {:tag :Items},
            :kids  [{:attrs {:tag :Item},
                     :kids  [{:attrs {:tag :Type}, :value "A"}
                             {:attrs {:tag :Note}, :value "AA1"}]}
                    {:attrs {:tag :Item},
                     :kids  [{:attrs {:tag :Type}, :value "B"}
                             {:attrs {:tag :Note}, :value "BB1"}]}
                    {:attrs {:tag :Item},
                     :kids  [{:attrs {:tag :Type}, :value "C"}
                             {:attrs {:tag :Note}, :value "CC1"}]}
                    {:attrs {:tag :Item},
                     :kids  [{:attrs {:tag :Type}, :value "A"}
                             {:attrs {:tag :Note}, :value "AA2"}]}]}]})

The final code fragment removes Type="B" or Type="C" nodes:

type-bc-hid?    (fn [hid] (pos? (count (glue
                            (find-leaf-hids hid [:** :Type] "B")
                            (find-leaf-hids hid [:** :Type] "C")))))

type-bc-hids    (find-hids-with root-hid [:** :Item] type-bc-hid?)
>>              (apply remove-hid type-bc-hids)
tree-3          (hid->tree root-hid)
tree-3-hiccup   (hid->hiccup root-hid) ]

yielding the final result tree shown in both tree format and hiccup format:

(is= tree-3
  {:attrs {:tag :ROOT},
   :kids
          [{:attrs {:tag :Items},
            :kids  [{:attrs {:tag :Item},
                     :kids  [{:attrs {:tag :Type}, :value "A"}
                             {:attrs {:tag :Note}, :value "AA1"}]}
                    {:attrs {:tag :Item},
                     :kids  [{:attrs {:tag :Type}, :value "A"}
                             {:attrs {:tag :Note}, :value "AA2"}]}]}]})
(is= tree-3-hiccup
  [:ROOT
   [:Items
    [:Item [:Type "A"] [:Note "AA1"]]
    [:Item [:Type "A"] [:Note "AA2"]]]]))))

The full example can be found in the forest-examples unit test.

Update

Here is the most compact version with extra features removed:

(dotest
  (with-forest (new-forest)
    (let [xml-str         "
                            
                              AAA1
                              BBB1
                              CCC1
                              AAA2
                            
                          "
          enlive-tree     (->> xml-str
                            java.io.StringReader.
                            en-html/xml-resource
                            first)
          root-hid        (add-tree-enlive enlive-tree)
          blank-leaf-hid? (fn [hid] (ts/whitespace? (hid->value hid)))
          has-bc-leaf?    (fn [hid] (or (has-child-leaf? hid [:** :Type] "B")
                                        (has-child-leaf? hid [:** :Type] "C")))
          blank-leaf-hids (keep-if blank-leaf-hid? (all-leaf-hids))
          >>              (apply remove-hid blank-leaf-hids)
          bc-item-hids    (find-hids-with root-hid [:** :Item] has-bc-leaf?)]
      (apply remove-hid bc-item-hids)
      (is= (hid->hiccup root-hid)
        [:ROOT
         [:Items
          [:Item [:Type "A"] [:Note "AA1"]]
          [:Item [:Type "A"] [:Note "AA2"]]]]))))