e168f08 - Latest Comments in Assignment 1

Re: Assignment 1

jgn — Sun, 05 Oct 2008 16:22:47 -0000

Review your code again. If you have to, try commenting out methods until it doesn't show the error.

Re: Assignment 1

sa — Sun, 05 Oct 2008 15:32:21 -0000

I've lookded into that. Apparently all blocks are ended fine and I tried changing the location of solution to the 'other' folder, but the same error.

Re: Assignment 1

jgn — Sun, 05 Oct 2008 15:09:10 -0000

"syntax error, unexpected $end, expecting kEND"

Look at your code and verify that all blocks are ended correctly.

Re: Assignment 1

sa — Sun, 05 Oct 2008 14:55:40 -0000

I am having this output when i run the solution test.

C:\assn1-1.0.0\test\other>ruby solution_set_test.rb
C:/Ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_re
quire': C:/assn1-1.0.0/student_solution_set.rb:244: syntax error, unexpected $en
d, expecting kEND (SyntaxError)
from C:/Ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `re
quire'
from solution_set_test.rb:4

Re: Assignment 1

jgn — Fri, 03 Oct 2008 13:48:48 -0000

1. No. You cannot assume that if you pass all tests, you'll get 100%. Two reasons:

a. You may write a solution that ONLY passes the tests. You need to write code that satisfies the requirements, which we stated in words and sentences. The tests may help, but it is entirely possible that the data we use in the tests misses an edge case.

b. Code that passes the tests may be grossly inefficient, inelegant, relying on regular expressions, etc.

2. No. Pick your ten best and submit those. Comment out the solutions for the ones you don't want to submit.

If you solve all twelve, we will pick 10 according to any rule that pops into our heads at the moment (randomly; first 10; easiest to grade; whatever).

Re: Assignment 1

rajatbaner — Fri, 03 Oct 2008 13:41:20 -0000

Regarding Grading,
- If our code passes all the tests in the solution_set_test.rb, can we assume we'll get 100% ?
- if there are extra tests with some weird cases we have not accounted for, we'll lose points. If so, can we turn in all 12, and the grader will drop the lowest two problems?

Thanks!

Re: Assignment 1

LanceB — Fri, 03 Oct 2008 13:28:47 -0000

Excellent. That is exactly what I was looking for!

Re: Assignment 1

jgn — Fri, 03 Oct 2008 13:16:18 -0000

collect means: Invokes block once for each element

So ONE element should get passed into the block. You have two block parameters, so that is not right.

The classic way to have some value "accrue" is with inject. E.g.,

>> [ 1, 2, 3 ].inject(5) { |m, e| m += e }
=> 11

Here I'm starting the memo (m) off at 5, and am adding each element (1, 2, 3) to the memo successively.

This might provide more clarity:

>> [ 1, 2, 3 ].inject(5) { |m, e| m += e; puts "total so far: #{m}"; m }
total so far: 6
total so far: 8
total so far: 11
=> 11

Re: Assignment 1

LanceB — Fri, 03 Oct 2008 13:09:08 -0000

I am sure this is probably ridiculously obvious but I am having a terrible time trying to get a counter started in a block so that I can execute an if statement based upon its value. Is there a way to pass the initial value without the inject method? I have tried something like this but the values never increase even though an array shows that it did indeed loop through the array:

a.collect {|val, counter| counter += 1; print counter.to_s}

Help!

Re: Assignment 1

jgn — Fri, 03 Oct 2008 12:44:19 -0000

I am not sure what you mean by "swallowed up."

Notice:

h = {"hither"=>2, "baz"=>1, "foo"=>500}
p h.sort {|a,b| puts b; a[1]<=>b[1]}

results in:

[["baz", 1], ["hither", 2], ["foo", 500]]

OK? I don't see anything getting "swallowed up."

If you like, e-mail your implementation of problem 6 to your TA/grader.

Re: Assignment 1

akv — Fri, 03 Oct 2008 11:21:18 -0000

Ok, I was trying to sort an array by val, then flatten it and to a diff with the hash values but my hash keeps getting re-written. Does that maake sense or should I rethink my strategy. I guess either way could you exmplain what the line is doing h.sort {|a,b| a[1]<=>b[1]} and why my pieces of my hash are getting gobbled up?

Re: Assignment 1

jgn — Fri, 03 Oct 2008 09:16:20 -0000

you should think very, very hard about what you are trying to do. What do you think "sorting a hash" means? Note that a hash has keys and values. Do you want to sort by the keys or the values? Also note that a hash is unordered. The result of "sorting" a hash is an array of arrays. Is that what you want?

I would recommend reassessing your basic strategy in light of the problem.

Re: Assignment 1

akv — Thu, 02 Oct 2008 23:06:55 -0000

sorry, i am looking for a little frther clarification with the line h.sort {|a,b| a[1]<=>b[1]}

Also, if I use the following hash - h = { "a" => 20, "b" => 30, "c" => 10 } - then the hash does not get modified when I run the sort on the line above, but if I use the has in the hw problem, then 2 of the elements get dropped?

Re: Assignment 1

akv — Thu, 02 Oct 2008 23:05:00 -0000

Hi,

When I replace the code int he pixaxe f

h = { "a" => 20, "b" => 30, "c" => 10 }
h.sort {|a,b| a[1]<=>b[1]}

h.sort {|a,b| a[1]<=>b[1]}
with code pertinent to problem 6, then some of the values in the hash get dropped? Can someone explain a little more what the folowing line does

Re: Assignment 1

jgn — Wed, 01 Oct 2008 17:11:51 -0000

There may be an over-the-counter medication that can help with that.

Re: Assignment 1

vaughanatworld — Wed, 01 Oct 2008 17:06:34 -0000

I think I just had an epiphany.

Re: Assignment 1

jgn — Wed, 01 Oct 2008 16:50:29 -0000

If you think you need more block parameters, then you should be writing the code that does the enumeration yourself -- you are probably no longer in the realm of using utility methods such as .inject, .map, etc.

I.e., write the method that does the yield.

Re: Assignment 1

vaughanatworld — Wed, 01 Oct 2008 16:46:28 -0000

On block parameters, for Enumerable#inject there is |memo, obj| . From the context of what you are saying above, is it possible to get memo1, memo2 ... ? I can force it with array of arrays etc but it would be nice to short circuit this with user created block parameters. Is this possible?

Re: Assignment 1

jgn — Sun, 28 Sep 2008 23:09:34 -0000

We can definite correlate the "@" one, so use that.

Re: Assignment 1

swithin — Sun, 28 Sep 2008 22:08:27 -0000

Harvard has assigned me two ID #s, neither of which are named "student id number".

One is named "Harvard ID (HUID)", and the other is named just plain "ID Number", which starts with an "@" sign.

Which one should we use for the "student id number" on homework assignment 1?

def info_student_id
""
end

Re: Assignment 1

plu — Sun, 28 Sep 2008 11:38:51 -0000

Yes. I know that. :)

I am just going through irb and trying out all the methods to see if my understandings of each method is valid - it was just part of the exercise that I came across these two methods.

Thanks!

Re: Assignment 1

jgn — Sun, 28 Sep 2008 07:56:30 -0000

Just FYI: Good solutions can be expressed for all of the assigned problems without using each_sice and each_cons.

Re: Assignment 1

plu — Sun, 28 Sep 2008 00:50:54 -0000

Found my own answer at http://codesnippets.joyent....

Quotes from the website:
"Rdoc is causing some serious confusion with libraries.

In core documentation, Enumerable defines each_slice method.

Extend this module into your class and each_slice is not defined.

Reason? each_slice is NOT in the core Enumerable module, but rather the Standard Library Enumerable::Enumerator class, even though the ruby-doc core class documents say otherwise.

You must

require 'enumerator'

to have each_slice is available as a method to your class."

Re: Assignment 1

plu — Sun, 28 Sep 2008 00:44:03 -0000

Hmm. I actually got it to work when typing in

require 'enumerator'

within irb. Why is this the case? Thanks!

Re: Assignment 1

plu — Sun, 28 Sep 2008 00:37:41 -0000

The method each_slice and each_cons seem to be defined within the Enumerable. However, when I am invoking it, it tells me "NoMethodError: undefined method' - this occurs for both Array and Range. Even if I use the sample line from the documentation

e.g.
(1..10).each_slice(3) {|a| p a}

It still throws an error. Are these methods not valid? Thanks!