Minimum value in a vector

[Don]

I am having difficulty approaching this problem. I'm not sure if it
can be done in one swoop, or requires a few steps.

I have 5 vectors as such:

a [2 4 6 7]
b [1 3 9 2]
c [2 4 5 6]
d [6 1 3 8]
e [4 8 2 1]

And I want to take the minimum value at a given index between the
vectors. Therefore, minimum value at index 0 would yield the value 1
from vector b.

Thank You.

[Stefan Kamphausen]

Hi,

a quick shot would be

(reduce min (map #(get % 0) (list a b c d e)))

It would be nicer to have a vector of vectors or a list of vectors at
the beginning, probably.

Cheers,
Stefan

[Kevin Downey]

user=> (vec (map min [2 4 6 7] [1 3 9 2] [2 4 5 6] [6 1 3 8] [4 8 2 1]))
[1 1 2 1]
user=>

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--
And what is good, Phaedrus,
And what is not good—
Need we ask anyone to tell us these things?

[Don]

Thank you Stefan and Kevin. Awesome solutions that answer my
question. However I actually made a mistake in posing my question.
Let me attempt to ask my question again.

I have 5 vectors as such:
a [2 4 6 7]
b [1 3 9 2]
c [2 4 5 6]
d [6 1 3 8]
e [4 8 2 1]

and the output i want is this

a1 [0 0 0 0]
b1 [1 0 0 0]
c1 [0 0 0 0]
d1 [0 1 0 0]
e1 [0 0 1 1]

Now I'm not sure if it can be done in one swoop, or should be done in
a loop. I was thinking a loop, but I'm having trouble thinking about
it.

I initially thought of creating a function that takes in 5 vectors and
returns a single vector. So the first time its called it would
return a1 [0 0 0 0] then call it again and return b1 [1 0 0 0] etc...
I know it will repeat calculations however I couldn't come up with
anything else.

Thank you.

[Don]

Forgot to mention that i'm still calculating the minimum distance
between the vectors, but my output isn't actually the minimum value.
The output is the minimum value in terms of the vectors, if that makes
sense.

[Wilson MacGyver]

assuming, vector a b c d e are already defined.

I'd do

user=> (map vector a b c d e)
([2 1 2 6 4] [4 3 4 1 8] [6 9 5 3 2] [7 2 6 8 1])

you can then use the solutions provided from previous messages
to find the min value of each vector.

so you then end up with

[0 1 0 0 0] [0 0 0 1 0] [0 0 0 0 1] [0 0 0 0 1]

at that point, you repeat the same trick

(map vector [0 1 0 0 0] [0 0 0 1 0] [0 0 0 0 1] [0 0 0 0 1])

and that will give you

[0 0 0 0] [1 0 0 0] [0 0 0 0] [0 1 0 0] [0 0 1 1]

Omnem crede diem tibi diluxisse supremum.

[Don]

I still can't figure it out. If have this set.

a [2 4 6 7]
b [1 3 9 2]
c [2 4 5 6]
d [6 1 3 8]
e [4 8 2 1]

If I do (reduce min (map #(get % 0) (list a b c d e)))

It grabs the min value from index 0 of the five vectors and returns 1
corresponding to 'b'. But I'm not sure how I would determine it's
coming from 'b'. I need to know that it comes from 'b' in order to
build the new vector.

If I do (vec (map min a b c d e))

It grabs the min value from index (0, 1, 2, 3) and puts it in a vector

[1 1 2 1]

And I don't know from what vector the minimum value is coming from.

The solution is probably already here but I can't think of it. Sorry.

[John Harrop]

(defn min-col [col vecs]

  (apply min (map #(nth % col) vecs)))

user=> (min-col 0 [[2 4 6 7] [1 3 9 2] [2 4 5 6] [6 1 3 8] [4 8 2 1]])

1

[John Harrop]

On Wed, Dec 2, 2009 at 7:59 PM, Don <josere...@gmail.com> wrote:

I still can't figure it out.  If have this set.

 a [2 4 6 7]
 b [1 3 9 2]
 c [2 4 5 6]
 d [6 1 3 8]
 e [4 8 2 1]

If I do (reduce min (map #(get % 0) (list a b c d e)))

It grabs the min value from index 0 of the five vectors and returns 1
corresponding to 'b'. But I'm not sure how I would determine it's
coming from 'b'.  I need to know that it comes from 'b' in order to
build the new vector.

If I do (vec (map min a b c d e))

It grabs the min value from index (0, 1, 2, 3) and puts it in a vector

[1 1 2 1]

And I don't know from what vector the minimum value is coming from.

The solution is probably already here but I can't think of it.  Sorry.

 

(defn min-col [col vecs]

  (apply min (map #(nth % col) vecs)))

(defn min-pos [col vecs]

  (let [m (min-col col vecs)]

    (map #(if (= m %) 1 0) (map #(nth % col) vecs))))

(defn min-pos-vecs [vecs]

  (apply map vector

    (map #(min-pos % vecs)

      (range (count (first vecs))))))

user=> (min-pos-vecs [[2 4 6 7] [1 3 9 2] [2 4 5 6] [6 1 3 8] [4 8 2 1]])

([0 0 0 0] [1 0 0 0] [0 0 0 0] [0 1 0 0] [0 0 1 1])

[Wilson MacGyver]

(defn min-dist [coll]
(let [minval (reduce min coll)]
(map #(if (= minval %) 1 0) coll)))

this function, if you pass
user=> (min-dist [2 1 2 6 4])
(0 1 0 0 0)

assume the 5 vectors are stored in a b c d e.

user=> (apply map vector (map min-dist (map vector a b c d e)))
([0 0 0 0] [1 0 0 0] [0 0 0 0] [0 1 0 0] [0 0 1 1])

On Wed, Dec 2, 2009 at 7:59 PM, Don <josere...@gmail.com> wrote:

[Chouser]

>> On Wed, Dec 2, 2009 at 6:22 PM, Don <josereyno...@gmail.com> wrote:
>> > Thank you Stefan and Kevin.  Awesome solutions that answer my
>> > question.  However I actually made a mistake in posing my question.
>> > Let me attempt to ask my question again.
>>
>> >  I have 5 vectors as such:
>> >  a [2 4 6 7]
>> >  b [1 3 9 2]
>> >  c [2 4 5 6]
>> >  d [6 1 3 8]
>> >  e [4 8 2 1]
>>
>> > and the output i want is this
>>
>> > a1 [0 0 0 0]
>> > b1 [1 0 0 0]
>> > c1 [0 0 0 0]
>> > d1 [0 1 0 0]
>> > e1 [0 0 1 1]

(defn min-cols [v]
(map #(apply min-key % (range (count v)))
(apply map vector v)))

(defn mark-cols [v m]
(map (fn [i] (map #(if % 1 0) (map = m (repeat (count m) i))))
(range (count v))))

(def v [[2 4 6 7] [1 3 9 2] [2 4 5 6] [6 1 3 8] [4 8 2 1]])

user=> (mark-cols v (min-cols v))
((0 0 0 0) (1 0 0 0) (0 0 0 0) (0 1 0 0) (0 0 1 1))

--Chouser

[Don]

Thanks to everyone for the solutions. I actually wrote this terribly
ugly function. Terrible. This should go in the "don't write code like
this section" in clojure book.

(defn md2 [d1 d2 d3 d4 d5]
(let [cnt (count d1)]
(loop [i 0 v []]
(if (= i cnt)
v
(do
(if (= (get d1 i) (reduce min (map #(get % i) (list d1 d2 d3
d4 d5))))
(recur (inc i) (conj v 1))
(recur (inc i) (conj v 0))))))))