I'm trying to write some code that will take an array of numbers and print a string representation of the range of the numbers.
def rng (arr)
str = arr[0].to_s
idx = 1
arr.each do |i|
next if arr.index(i) == 0
if arr[arr.index(i)-1] == i - 1
unless str[idx - 1] == "-"
str[idx] = "-"
#else next
end
#puts "if statement str: #{str}, idx: #{idx}"
else
str[idx] = arr[arr.index(i)-1].to_s
idx += 1
str[idx] = ","+ i.to_s
end
idx += 1
end
puts "str = #{str} and idx = #{idx}"
end
rng [0, 1, 2, 3, 8] #"0-3, 8"
I get this error:
arrayRange_0.rb:9:in `[]=': index 3 out of string (IndexError)
Can anyone explain why? When I uncomment the else next it works. Not sure why.
When you get that error, str contains the value 0- which is only 2 characters long - therefore it can't be indexed to the position of 3.
Add this line before line 9, which is causing your error:
puts "str = #{str}, idx = #{idx}"
It will output:
str = 0, idx = 1
str = 0-, idx = 3
Here is how you could do it:
def rng(arr)
ranges = []
arr.each do |v|
if ranges.last && ranges.last.include?(v-1)
# If this is the next consecutive number
# store it in the second element
ranges.last[1] = v
else
# Add a new array with current value as the first number
ranges << [v]
end
end
# Make a list of strings from the ranges
# [[0,3], [8]] becomes ["0-3", "8"]
range_strings = ranges.map{|range| range.join('-') }
range_strings.join(', ')
end
p rng [0, 1, 2, 3, 8]
# results in "0-3, 8"
Like the previous answer says, your index is outside of the string
Related
I'm trying to work through a level 5 kata by using while loops. Essentially the problem is to turn each letter rotors[n] number of times and then move on to the next rotors number until you get an output word.
flap_display(["CAT"],[1,13,27])
should output ["DOG"]
Here's what I have so far
def flap_display(lines, rotors)
stuff = "ABCDEFGHIJKLMNOPQRSTUVWXYZ?!##&()|<>.:=-+*/0123456789"
i = 0
j = 0
new_word = lines
while i < rotors.length
while j < new_word[0].length
new_word[0][j] = stuff[stuff.index(new_word[0][j]) + rotors[i]]
j += 1
end
i += 1
j = 0
end
new_word
end
This technically traverses the stuff string and assigns the right letters. However it fails two important things: it does not skip each letter when it rotates to the correct position (C should stop rotating when it hits D, A when it hits O etc) and it does not account for reaching the end of the stuff list and eventually returns a nil value for stuff[stuff.index(new_word[0][j]) + rotors[i]]. How can I fix these two problems using basic loops and enumerables or maybe a hash?
A fuller statement of the problem is given here. This is one Ruby-like way it could be done.
FLAPS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ ?!##&()|<>.:=-+*/0123456789"
NBR_FLAPS = FLAPS.size
def flap_display(str, rot)
rot_cum = rot.each_with_object([]) { |n,a| a << a.last.to_i + n }
str.gsub(/./) { |c| FLAPS[(c.ord + rot_cum.shift - 65) % NBR_FLAPS] }
end
flap_display("CAT", [1,13,27])
#=> "DOG"
flap_display("DOG", [-1,-13,-27])
#=> "CAT"
flap_display("CAT", [5,37,24])
#=> "H*&"
'A'.ord #=> 65 and rot_cum contains the cumulative values of rot:
arr = [1, 13, 27]
rot_cum = arr.each_with_object([]) { |n,a| a << a.last.to_i + n }
#=> [1, 14, 41]
I've written a.last.to_i rather than a.last to deal with the case where a is empty, so a.last #=> nil, meaning a.last.to_i => nil.to_i => 0. See NilClass#to_i. Those opposed to such trickery could write:
rot_cum = arr.drop(1).each_with_object([arr.first]) { |n,a| a << a.last + n }
The below code is my newbie take on a bubble sort method.
#For each element in the list, look at that element and the element
#directly to it's right. Swap these two elements so they are in
#ascending order.
def bubble_sort (array)
a = 0
b = 1
until (array.each_cons(2).all? { |a, b| (a <=> b) <= 0}) == true do
sort = lambda {array[a] <=> array[b]}
sort_call = sort.call
loop do
case sort_call
when -1 #don't swap
a += 1
b += 1
break
when 0 #don't swap
a += 1
b += 1
break
when 1 #swap
array.insert(a,array.delete_at(b))
a += 1
b += 1
break
else #end of array, return to start
a = 0
b = 1
break
end
end
end
puts array.inspect
end
array = [4, 2, 5, 6, 3, 23, 5546, 234, 234, 6]
bubble_sort(array)
I want to be able to alter this method so that it takes a block of code as an argument and uses this to determine how it sorts.
For example:
array = ["hello", "my", "name", "is", "daniel"]
bubble_sort(array) {array[#a].length <=> array[#b].length}
(When I've tried this I've turned a and b into instance variables throughout the code.)
I have tried using yield but I get undefined method 'length' for nil:NilClass once the end of the array is reached. I've tried adding in things such as
if array[#b+1] == nil
#a = 0
#b = 1
end
This helps but I still end up with weird problems like infinite loops or not being able to sort more than certain amount of elements.
Long story short, I have been at this for hours. Is there a simple way to do what I want to do? Thanks.
The way you're calling your lambda is a bit odd. It's actually completely unnecessary. I refactored your code and cleaned up a bit of the redundancy. The following works for me:
def sorted?(arr)
arr.each_cons(2).all? { |a, b| (a <=> b) <= 0 }
end
def bubble_sort (arr)
a = 0
b = 1
until sorted?(arr) do
# The yield call here passes `arr[a]` and `arr[b]` to the block.
comparison = if block_given?
yield(arr[a], arr[b])
else
arr[a] <=> arr[b]
end
if [-1, 0, 1].include? comparison
arr.insert(a, arr.delete_at(b)) if comparison == 1
a += 1
b += 1
else
a = 0
b = 1
end
end
arr
end
sample_array = [4, 2, 5, 6, 3, 23, 5546, 234, 234, 6]
# Sanity check:
100.times do
# `a` is the value of `arr[a]` in our function above. Likewise for `b` and `arr[b]`.
print bubble_sort(sample_array.shuffle) { |a, b| a <=> b }, "\n"
end
EDIT
A cleaner version:
# In place swap will be more efficient as it doesn't need to modify the size of the arra
def swap(arr, idx)
raise IndexError.new("Index #{idx} is out of bounds") if idx >= arr.length || idx < 0
temp = arr[idx]
arr[idx] = arr[idx + 1]
arr[idx + 1] = temp
end
def bubble_sort(arr)
loop do
sorted_elements = 0
arr.each_cons(2).each_with_index do |pair, idx|
comparison = if block_given?
yield pair.first, pair.last
else
pair.first <=> pair.last
end
if comparison > 0
swap(arr, idx)
else
sorted_elements += 1
end
end
return arr if sorted_elements >= arr.length - 1
end
end
# A simple test
sample_array = [4, 2, 2, 2, 2, 2, 5, 5, 6, 3, 23, 5546, 234, 234, 6]
sample_str_array = ["a", "ccc", "ccccc"]
100.times do
print bubble_sort(sample_array.shuffle) { |a, b| a <=> b }, "\n"
print bubble_sort(sample_str_array.shuffle) { |a, b| a.length <=> b.length }, "\n"
end
You're not too far off. Just a few things:
Make your function take a block argument
def bubble_sort (array, &block)
Check to see if the user has provided a block
if block_given?
# Call user's comparator block
else
# Use the default behavior
end
Call the user's comparator block
block.call(a, b)
In the user-provided block, accept block params for the elements to compare
bubble_sort(array) {|a,b| a.length <=> b.length}
That should put you in the right ballpark.
# Write a method that takes in a string. Your method should return the
# most common letter in the array, and a count of how many times it
# appears.
#
# Difficulty: medium.
def most_common_letter(string)
letter = 0
letter_count = 0
idx1 = 0
mostfreq_letter = 0
largest_letter_count = 0
while idx1 < string.length
letter = string[idx1]
idx2 = 0
while idx2 < string.length
if letter == string[idx2]
letter_count += 1
end
idx2 += 1
end
if letter_count > largest_letter_count
largest_letter_count = letter_count
mostfreq_letter = letter
end
idx1 += 1
end
return [mostfreq_letter, largest_letter_count]
end
# These are tests to check that your code is working. After writing
# your solution, they should all print true.
puts(
'most_common_letter("abca") == ["a", 2]: ' +
(most_common_letter('abca') == ['a', 2]).to_s
)
puts(
'most_common_letter("abbab") == ["b", 3]: ' +
(most_common_letter('abbab') == ['b', 3]).to_s
)
So in my mind the program should set a letter and then once that is set cycle through the string looking for letters that are the same, and then once there is one it adds to letter count and then it judges if its the largest letter count and if it is those values are stored to the eventual return value that should be correct once the while loop ends. However I keep getting false false. Where am I going wrong?
Your code does not return [false, false] to me; but it does return incorrect results. The hint by samgak should lead you to the bug.
However, for a bit shorter and more Rubyish alternative:
def most_common_letter(string)
Hash.new(0).tap { |h|
string.each_char { |c| h[c] += 1 }
}.max_by { |k, v| v }
end
Create a new Hash that has a default value of 0 for each entry; iterate over characters and count the frequency for each of them in the hash; then find which hash entry is the largest. When a hash is iterated, it produces pairs, just like what you want for your function output, so that's nice, too.
The array counts is as follows:
counts = ["a", 1]
What does this:
counts[0][0]
refer to?
I've only seen this before:
array[idx]
but never this:
array[idx][idx]
where idx is an integer.
This is the entire code where the snippet of code before was from:
def num_repeats(string) #abab
counts = [] #array
str_idx = 0
while str_idx < string.length #1 < 4
letter = string[str_idx] #b
counts_idx = 0
while counts_idx < counts.length #0 < 1
if counts[counts_idx][0] == letter #if counts[0][0] == b
counts[counts_idx][1] += 1
break
end
counts_idx += 1
end
if counts_idx == counts.length #0 = 0
# didn't find this letter in the counts array; count it for the
# first time
counts.push([letter, 1]) #counts = ["a", 1]
end
str_idx += 1
end
num_repeats = 0
counts_idx = 0
while counts_idx < counts.length
if counts[counts_idx][1] > 1
num_repeats += 1
end
counts_idx += 1
end
return counts
end
The statement
arr[0]
Gets the first item of the array arr, in some cases this may also be an array (Or another indexable object) this means you can get that object and get an object from that array:
# if arr = [["item", "another"], "last"]
item = arr[0]
inner_item = item[0]
puts inner_item # => "item"
This can be shortened to
arr[0][0]
So any 2 dimensional array or array containing indexable objects can work like this, e.g. with an array of strings:
arr = ["String 1", "Geoff", "things"]
arr[0] # => "String 1"
arr[0][0] # => "S"
arr[1][0] # => "G"
It's for nested indexing
a = [ "item 0", [1, 2, 3] ]
a[0] #=> "item 0"
a[1] #=> [1, 2, 3]
a[1][0] #=> 1
Since the value at index 1 is another array you can use index referencing on that value as well.
EDIT
Sorry I didn't thoroughly read the original question. The array in question is
counts = ["a", 1]
In this case counts[0] returns "a" and since we can use indexes to references characters of a string, the 0th index in the string "a" is simply "a".
str = "hello"
str[2] #=> "l"
str[1] #=> "e"
Is there a built in way of printing a readable matrix in Ruby?
For example
require 'matrix'
m1 = Matrix[[1,2], [3,4]]
print m1
and have it show
=> 1 2
3 4
in the REPL instead of:
=> Matrix[[1,2][3,4]]
The Ruby Docs for matrix make it look like that's what should show happen, but that's not what I'm seeing. I know that it would be trivial to write a function to do this, but if there is a 'right' way I'd rather learn!
You could convert it to an array:
m1.to_a.each {|r| puts r.inspect}
=> [1, 2]
[3, 4]
EDIT:
Here is a "point free" version:
puts m1.to_a.map(&:inspect)
I couldn't get it to look like the documentation so I wrote a function for you that accomplishes the same task.
require 'matrix'
m1 = Matrix[[1,2],[3,4],[5,6]]
class Matrix
def to_readable
i = 0
self.each do |number|
print number.to_s + " "
i+= 1
if i == self.column_size
print "\n"
i = 0
end
end
end
end
m1.to_readable
=> 1 2
3 4
5 6
Disclaimer: I'm the lead developer for NMatrix.
It's trivial in NMatrix. Just do matrix.pretty_print.
The columns aren't cleanly aligned, but that'd be easy to fix and we'd love any contributions to that effect.
Incidentally, nice to see a fellow VT person on here. =)
You can use the each_slice method combined with the column_size method.
m1.each_slice(m1.column_size) {|r| p r }
=> [1,2]
[3,4]
Ok, I'm a total newbie in ruby programming. I'm just making my very first incursions, but it happens I got the same problem and made this quick'n'dirty approach.
Works with the standard Matrix library and will print columns formatted with same size.
class Matrix
def to_readable
column_counter = 0
columns_arrays = []
while column_counter < self.column_size
maximum_length = 0
self.column(column_counter).each do |column_element|# Get maximal size
length = column_element.to_s.size
if length > maximal_length
maximum_length = length
end
end # now we've got the maximum size
column_array = []
self.column(column_counter).each do |column_element| # Add needed spaces to equalize each column
element_string = column_element.to_s
element_size = element_string.size
space_needed = maximal_length - element_size +1
if space_needed > 0
space_needed.times {element_string.prepend " "}
if column_counter == 0
element_string.prepend "["
else
element_string.prepend ","
end
end
column_array << element_string
end
columns_arrays << column_array # Now columns contains equal size strings
column_counter += 1
end
row_counter = 0
while row_counter < self.row_size
columns_arrays.each do |column|
element = column[row_counter]
print element #Each column yield the correspondant row in order
end
print "]\n"
row_counter += 1
end
end
end
Any correction or upgrades welcome!
This is working for me
require 'matrix'
class Matrix
def print
matrix = self.to_a
field_size = matrix.flatten.collect{|i|i.to_s.size}.max
matrix.each do |row|
puts (row.collect{|i| ' ' * (field_size - i.to_s.size) + i.to_s}).join(' ')
end
end
end
m = Matrix[[1,23,3],[123,64.5, 2],[0,0,0]]
m.print
Here is my answer:
require 'matrix'
class Matrix
def to_pretty_s
s = ""
i = 0
while i < self.column_size
s += "\n" if i != 0
j = 0
while j < self.row_size
s += ' ' if j != 0
s += self.element(i, j).to_s
j += 1
end
i += 1
end
s
end
end
m = Matrix[[0, 3], [3, 4]]
puts m # same as 'puts m.to_s'
# Matrix[[0, 3], [3, 4]]
puts m.to_pretty_s
# 0 3
# 3 4
p m.to_pretty_s
# "0 3\n3 4"
You could use Matrix#to_pretty_s to get a pretty string for format.
There is no inbuilt Ruby way of doing this. However, I have created a Module which can be included into Matrix that includes a method readable. You can find this code here, but it is also in the following code block.
require 'matrix'
module ReadableArrays
def readable(factor: 1, method: :rjust)
repr = to_a.map { |row|
row.map(&:inspect)
}
column_widths = repr.transpose.map { |col|
col.map(&:size).max + factor
}
res = ""
repr.each { |row|
row.each_with_index { |el, j|
res += el.send method, column_widths[j]
}
res += "\n"
}
res.chomp
end
end
## example usage ##
class Matrix
include ReadableArrays
end
class Array
include ReadableArrays
end
arr = [[1, 20, 3], [20, 3, 19], [-32, 3, 5]]
mat = Matrix[*arr]
p arr
#=> [[1, 20, 3], [20, 3, 19], [-2, 3, 5]]
p mat
#=> Matrix[[1, 20, 3], [20, 3, 19], [-2, 3, 5]]
puts arr.readable
#=>
# 1 20 3
# 20 3 19
# -32 3 5
puts mat.readable
#=>
# 1 20 3
# 20 3 19
# -32 3 5
puts mat.readable(method: :ljust)
#=>
# 1 20 3
# 20 3 19
# -32 3 5
puts mat.readable(method: :center)
#=>
# 1 20 3
# 20 3 19
# -32 3 5
I had this problem just yet and haven't seen anyone posting it here, so I will put my solution if it helps someone. I know 2 for loops are not the best idea, but for smaller matrix it should be okay, and it prints beautifully and just how you want it, also without of use of require 'matrix' nor 'pp'
matrix = Array.new(numRows) { Array.new(numCols) { arrToTakeValuesFrom.sample } }
for i in 0..numRows-1 do
for j in 0..numCols-1 do
print " #{matrix[i][j]} "
end
puts ""
end