Clojurians Log v2

hi @manutter51

I got another question

from: ch3 ex5.

I have this:

(def asym-hobbit-body-parts [{:name "head" :size 3}
                             {:name "left-eye" :size 1}
                             {:name "left-ear" :size 1}
                             {:name "mouth" :size 1}
                             {:name "nose" :size 1}
                             {:name "neck" :size 2}
                             {:name "left-shoulder" :size 3}
                             {:name "left-upper-arm" :size 3}
                             {:name "chest" :size 10}
                             {:name "back" :size 10}
                             {:name "left-forearm" :size 3}
                             {:name "abdomen" :size 6}
                             {:name "left-kidney" :size 1}
                             {:name "left-hand" :size 2}
                             {:name "left-knee" :size 2}
                             {:name "left-thigh" :size 4}
                             {:name "left-lower-leg" :size 3}
                             {:name "left-achilles" :size 1}
                             {:name "left-foot" :size 2}])


; 1st attempt works, but it ugly and repetitive
(reduce (fn [acc part]
          (let [n1 {:name (clojure.string/replace (:name part) #"^left-" "c1-")
                    :size (:size part)}
                n2 {:name (clojure.string/replace (:name part) #"^left-" "c2-")
                    :size (:size part)}]
            (conj acc n1 n2))) [] asym-hobbit-body-parts)

; 2nd attempt, close but doesnt work
(require '[clojure.string :as cs])

(defn radial-seq-part [part]
  "Given a part name, provide a lazy sequence of c1-name ... c5-name strings"
  (for [c-number (range 1 6)
        :let [new-name
              {:name (cs/replace (:name part) 
                                 #"^left-" (str "c" c-number "-"))
               :size (:size part)}]
        :when (re-find #"^left-" (:name part))]
    new-name))

(map radial-seq-part asym-hobbit-body-parts) ;> does c1...c5, but omits others

; 3rd attempt

in (defn radial-seq-part ... I’d like it to just pass the input part if that :when test fails

currently, it returns () when the string doesn’t match #"^left-"

Ok, let me just catch up on what’s in the B&T text for this…

;;;
; Problem 5
; Create a function that's similar to symmetrize-body-parts except that it has to
; work with weird space aliens with radial symmetry. Instead of two eyes, arms,
; legs, and so on, they have five.
;
; Create a function that generalizes symmetrize-body-parts and the function you
; created in Exercise 5. The new function should take a collection of body parts
; and the number of matching body parts to add. If you're completely new to Lisp
; languages and functional programming, it probably won't be obvious how to do
; this. If you get stuck, just move on to the next chapter and revisit the problem
; later.
;;;

Thanks!

Ok, I skimmed kinda quickly, the goal is to take a list of body parts, and return c1..c5 for all the “left” body parts?

yep

and in my code there attempt 1 works, and but I’m trying to be DRY

so I’m using for

and it returns the expected output for #"^left-"

but

it returns () for non regex matching inputs

I think I would probably use an if so if it starts with “left-” then return the c1..c5, otherwise return a vector with just the original part

so just if before the for

right

’ight. That’s not to bad. Thanks!

:thumbsup:

great it works, but it’s not flattened

(defn radial-seq-part [part]
  "Given a part, provide a lazy sequence of c1-name
   ... c5-name strings"
  (if (re-find #"^left-" (:name part))
    (for [c-number (range 1 6)
          :let [new-name
                {:name (cs/replace (:name part)
                                   #"^left-" (str "c" c-number "-"))
                 :size (:size part)}]
          :when (re-find #"^left-" (:name part))]
      new-name)
    part))

(map radial-seq-part asym-hobbit-body-parts) 

use mapcat instead of map

--->
({:name "head", :size 3}
 ({:name "c1-eye", :size 1}
  {:name "c2-eye", :size 1}
  {:name "c3-eye", :size 1}
  {:name "c4-eye", :size 1}
  {:name "c5-eye", :size 1})
 ({:name "c1-ear", :size 1}
  {:name "c2-ear", :size 1}
  {:name "c3-ear", :size 1}
  {:name "c4-ear", :size 1}
  {:name "c5-ear", :size 1})
 {:name "mouth", :size 1}
 {:name "nose", :size 1}
 {:name "neck", :size 2}
 ({:name "c1-shoulder", :size 3} ; and so on

I’ll check that out. ty!

mapcat flattens but the passed through parts from if are vectors not maps

([:name "head"]
 [:size 3]
 {:name "c1-eye", :size 1}
 {:name "c2-eye", :size 1}
 {:name "c3-eye", :size 1}; and so on...

I could -> flatten map

Try wrapping the mapcat with (into {} ...)

although hmm, not quite

(flatten (map … ) works

Does it? I thought flatten would give you something like (:name "head" :size 3 :name "c1-eye" :size 1...)

Oh well, I rarely use flatten, it’s probably just my ignorance

(def c1to5-body-parts
  (-> (map radial-seq-part asym-hobbit-body-parts)
      flatten))

; ==>
({:name "head", :size 3}
 {:name "c1-eye", :size 1}
 {:name "c2-eye", :size 1}
 {:name "c3-eye", :size 1}
 {:name "c4-eye", :size 1}
 {:name "c5-eye", :size 1}
 {:name "c1-ear", :size 1}
 {:name "c2-ear", :size 1}
 {:name "c3-ear", :size 1}
 {:name "c4-ear", :size 1}
 {:name "c5-ear", :size 1} and so on

awesome

so my sol’n is

(require '[clojure.string :as cs])

(defn radial-seq-part [part]
  "Given a part, provide a lazy sequence of c1-name
   ... c5-name strings"
  (if (re-find #"^left-" (:name part)) ; if it's a left- string
    (for [c-number (range 1 6) ; then return a lazy seqence
          :let [new-name
                {:name (cs/replace (:name part)
                                   #"^left-" (str "c" c-number "-"))
                 :size (:size part)}]
          :when (re-find #"^left-" (:name part))]
      new-name)
    part)) ; otherwise return the original part

(def c1to5-body-parts
  (-> (map radial-seq-part asym-hobbit-body-parts)
      flatten)) 

not to ugly. Thanks!

it’s the for that’s adding the extra nesting

because that’s a sequence of maps

so… it makes sense

that I need to flatten

I suppose :when is redundant

There’s one other thing you might try: on the line that says “otherwise return the original part”, instead of returning part return (list part). Then the unchanged parts will be inside a list just like the radial parts. Then go back to mapcat instead of map/flatten

(and yeah, you don’t need the :when now)

tried it,… still nested

what’s it look like?

oh nm, you’re right

(defn radial-seq-part [part]
  "Given a part, provide a lazy sequence of c1-name
   ... c5-name strings"
  (if (re-find #"^left-" (:name part)) ; if it's a left- string
    (for [c-number (range 1 6) ; then return a lazy seqence
          :let [new-name
                {:name (cs/replace (:name part)
                                   #"^left-" (str "c" c-number "-"))
                 :size (:size part)}]
          :when (re-find #"^left-" (:name part))] ;:when is redundant inside if
      new-name)
    (list part))) ; otherwise return the original part

(def c1to5-body-parts
  (mapcat radial-seq-part asym-hobbit-body-parts))

what happened there with the list?

So the idea is that for returns a list and part isn’t a list. So just wrap it in its own list, and voila, everything is a list

gotcha

so mapcat has consistent types

thanks again man!

I finished the book, and now I’m doing each chapters exercises…

cool

alright, that’s all for my day. See ya!

have a good one

Can you help me understand what’s happening here? https://www.braveclojure.com/core-functions-in-depth/#A_Vampire_Data_Analysis_Program_for_the_FWPD

(defn mapify
  "Return a seq of maps like {:name \"Edward Cullen\" :glitter-index 10}"
  [rows]
  (map (fn [unmapped-row]
         (reduce (fn [row-map [vamp-key value]]
                   (assoc row-map vamp-key (convert vamp-key value)))
                 {}
                 (map vector vamp-keys unmapped-row)))
       rows))

(defn mapify
  "Return a seq of maps like {:name \"Edward Cullen\" :glitter-index 10}"
  [rows]
  (map (fn [unmapped-row] ; this anonymous fn is mapped on all rows
         (reduce (fn [row-map [vamp-key value]] ; ???
                   (assoc row-map vamp-key (convert vamp-key value)))
                 {}
                 (map vector vamp-keys unmapped-row)))
       rows))

I’m working on ch. 4, ex. 3. where I’m supposed to create a similar set up for validation. However I don’t get this mapify This is what I have so far:

(def vamp-validators
  {:name #(not-empty %)
   :glitter-index #(> % 0)})

(defn validate-entry
 [vamp-key value]
 ((get vamp-validators vamp-key) value))

What kind of data is mapify being called on in the original example?

A CSV

and convert has keys that map to functions to parse string to int etc.

;;; Set up
; use absolute path to get around any issues with working directory.
(def filename "/Users/moo/Sync/braveandtrue/by-chapter/ch04-suspects.csv")

(def vamp-keys [:name :glitter-index])

(defn str->int
  [str]
  (Integer. str))

(def conversions {:name identity :glitter-index str->int})

(defn convert
  [vamp-key value]
  ((get conversions vamp-key) value))

(defn parse
  "Convert a CSV file into rows of columns"
  [string]
  (map #(clojure.string/split % #",")
       (clojure.string/split string #"\n")))

(defn mapify
  "Return a seq of maps like {:name \"Edward Cullen\" :glitter-index 10}"
  [rows]
  (map (fn [unmapped-row]
         (reduce (fn [row-map [vamp-key value]]
                   (assoc row-map vamp-key (convert vamp-key value)))
                 {}
                 (map vector vamp-keys unmapped-row)))
       rows))

(defn glitter-filter
  [minimum-glitter records]
  (filter #(>= (:glitter-index %) minimum-glitter) records))

(parse (slurp filename))

(def glitter-map
  (-> (slurp filename)
      parse
      mapify))

Hmm, I think I’m following.

I’m trying to write vamp-validators, validate-entry and validate. The latter of which is like mapify

but I don’t get mapify…

So for simplicity, let’s assume that vamp-keys is [:a :b :c :d] and we have a row that’s [1 2 3 4]. Calling map with multiple collections just takes an entry from each collection and passes the entries to whatever function you’re mapping with, in this case vector

So in our example, (map vector vamp-keys unmapped-row) is going to return [[:a 1] [:b 2] [:c 3] [:d 4]]

gotcha so (map vector vamp-keys unmapped-row) is taking

[:name :glitter-index] and ["bob" "10"] and returning {:name "bob" :glitter-index "10"}

Not quite

You have curly braces, I have square braces

[:name :glitter-index] and ["bob" "10"] and returning [:name "bob" :glitter-index "10"]

because this is input to vector

Right. You’re getting :key value, which looks like it should be in a map, but in this case we’re mapping vector over the entries, so we are just getting back a vector with a pair of entries

k, and this becomes input to reduce…

Right, each of those 2-element vectors is passed in as the 2nd arg to your reducing function

(The first arg is the map you’re accumulating)

Actually, I missed a slight mistake in your value, above

The map function isn’t going to return [:name "bob" :glitter-index "10"], it’s going to give you a list of 2-element vectors

i.e. '([:name "bob"] [:glitter-index "10"])

(defn mapify
  "Return a seq of maps like {:name \"Edward Cullen\" :glitter-index 10}"
  [rows]
  (map (fn [unmapped-row]
         ; reduce an anonymous function over our list of two element vectors
         ; ([:name "Bob"] [:glitter-index "10"])
         (reduce (fn [row-map [vamp-key value]]
                   (assoc row-map vamp-key (convert vamp-key value)))
                 {} ; reduce starts with an empty map
                 ; combine [:name :glitter-index] with input csv row data e.g. ["Bob" "10"]
                 ; to create ([:name "Bob"] [:glitter-index "10"])
                 (map vector vamp-keys unmapped-row)))
       rows))

That looks good — as a purist, I’d say to create '([:name "Bob"] [:glitter-index "10"])

so I’m following along … until reduce

without the single quote, it implies that you’re trying to call [:name "Bob"] as a function and passing [:glitter-index "10"] as an argument.

I see

It’s in a comment so it won’t break anything, but probably a good idea to get in the habit

Anyway, the reduce

You have {} as the initial value for what you’re trying to accumulate, and you’ve got a list like '([:name "Bob"] [:glitter-index "10"] ...) to iterate over

The first time thru, it’s going to call the reducing function with {} as the first argument, and [:name "Bob"] as the 2nd argument.

oh, so that’s why row-map is our first argument in the anon fn

Since you’ve got destructuring going on, that’s going to assign :name to vamp-key and "Bob" to value

right, row-map will be {} the first time thru

somehow I don’t see how it turns into a legit map

it seems like this ’ought to happen:

{:name “Bob”} {:glitter-index 10}

I assume convert is just looking up the key to do things like “Ok, :name should be a string, just return it, but :glitter-index should be a number, so parse the string and return the actual number” etc.

(def conversions {:name identity :glitter-index str->int})

(defn convert
  [vamp-key value]
  ((get conversions vamp-key) value))

it’s just type casting the number

Ok, cool, that’s what I expected

based on the key

So now inside the function, you’re calling (assoc row-map :name "Bob") (once convert is done converting it)

and that’s going to return {:name "Bob"}

I’m with ya

But this is reduce, not map, so that means the next time through, the first argument is going to be the result of the last time thru.

In other words, the 2nd time, we’re going to call the function with the arguments {:name "Bob"} and [:glitter-index "10"]

then, I’m imagining {:name “bob” :gl 2 :name “otherguy” :gl 3} which diesnt make sense

Yeah, it’s a little tricky, but that’s not what’s happening

what happens the 3rd time?

For each row, you only have each key once

:name "otherguy" is the next row

so that’s not part of the list that gets passed to the reduce — it’s a reduce nested inside a map

oh!

we’re just reducing two entries

then it’s back to getting mapped onto a new row

Well, if there’s only 2 entries per row, yes

reduce is operating on only one row

Right

and map is applying reduce row-by-row

a ha

great!

It would be easier to follow if you pulled the inner reduce out into its own function called convert-row-to-map or something

Then mapify would just be (defn mapify [rows] (map convert-row-to-map rows))

yes

true

Incidently, that’s a coding style I call “executable documentation” — when you read mapify, you know exactly what it’s doing because it says it’s converting rows to maps.

So sometimes it’s worth pulling out the inner stuff into a named function, because the name of the fn is good documentation for what it is you’re trying to do.

that makes sense. 🙂

so, I can imagine a few ways to make validators, but they don’t seem very slick

for example

I could just do ifs for name and glitter-index for an entry, then use map to apply it

however, I want this to return false right away

anyways, I ’ll go puzzle it out 🙂

thanks again man, that really helped!

:thumbsup:

is there an non macro version of and

trying to (apply and (false true false true))

if I use map with validation, I’ll get a lazy seq of booleans

I guess I can use some

there’s also every?

That’s probably what you want instead of apply and

great

this is what I came up with

(def vamp-validators
  {:name #(if (not-empty %) true false)
   :glitter-index #(>= % 0)})

(defn validate-element
  [vamp-key value]
  ((get vamp-validators vamp-key) value))

(defn validate-entry [entry]
  (not (some #(= false %)
      (for [foundkey (keys entry)]
        (validate-element foundkey (foundkey entry))))))
    ;    ((get vamp-validators foundkey) (foundkey entry))))))

(defn validate [entries]
  (not #(some #(= false %) (map validate-entry entries))))

cool, every is what I needed

(def vamp-validators
  {:name #(if (not-empty %) true false)
   :glitter-index #(>= % 0)})

(defn validate-element
  [vamp-key value]
  ((get vamp-validators vamp-key) value))

(defn validate-entry [entry]
  (every? true?
          (for [foundkey (keys entry)]
            (validate-element foundkey (foundkey entry)))))

(defn validate [entries]
  (every? true? (map validate-entry entries)))

Looks good — there’s some optimizations you can apply

You can replace (not-empty some-string) with (seq some-string)

(seq "a")
=> (\a)
(seq "")
=> nil

You can also replace every? true? just every? if you re-work your code a bit — there’s an implicit map inside every?, so you can do (every? validate-entry entries) for example

You can do the same sort of thing to get rid of the for, but it’s a bit tricker. Maybe you’d like to work that one out for yourself. 🙂