Fwd: Re: random number between 2 numbers

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Look at the Collections class hierarchy to understand the differences and choose the one which suits your needs. See also chapter 1 of the ”Basic Libraries Guide” manual in the “doc” directory of your VisualWorks installation.

 

HTH

Helge

Thanks,

I have read the document and I doubt between a Directonary or a Array.
I will test if the number ( 1- 16) can be a key for a Directonary or that I still can use something like "1@1" as key.

Roelof

 

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Roelof,

You can use anything you want as a dictionary key.  You could try representing your grid as an Array of Arrays. 

| grid |

grid := Array new.
grid add: (Array with: 1 with: 2).
grid add: (Array with: 3 with: 4).

To retrieve the value 2, inspect (grid first) last.

If you are coming from another language, an excellent start is the book Smalltalk by Example available here: http://stephane.ducasse.free.fr/FreeBooks.html

I am not a VW guy, but they may have a Matrix class.

Keep trying.

Thanks,

I have read the document and I doubt between a Directonary or a Array.
I will test if the number ( 1- 16) can be a key for a Directonary or that I still can use something like "1@1" as key.

Roelof

 

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On 4/11/2014 1:48 PM, Roelof Wobben wrote:

Roelof,

You can use anything you want as a dictionary key.  You could try representing your grid as an Array of Arrays. 

| grid |

grid := Array new.
grid add: (Array with: 1 with: 2).
grid add: (Array with: 3 with: 4).

To retrieve the value 2, inspect (grid first) last.

If you are coming from another language, an excellent start is the book Smalltalk by Example available here: http://stephane.ducasse.free.fr/FreeBooks.html

I am not a VW guy, but they may have a Matrix class.

Keep trying.

Thanks,
I will look at that book but at first glance I miss exercises.

What do you experts think of this book :  http://stephane.ducasse.free.fr/FreeBooks/InsideST/InsideSmalltalk.pdf

Roelof


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Hi Roelof,

 

A little more detail...

 

>> I have read the document and I doubt between a Directonary or a Array.
>> I will test if the number ( 1- 16) can be a key for a Directonary or that I still can use something like "1@1" as key.

 

Array can only be accessed with integer "keys", and only within the size allocated. Arrays don't grow in VisualWorks and most other Smalltalk dialects, so if you need growth then use an OrderedCollection instead of an Array. Both OC and Array will error if you attempt to access a position greater than the size allocated or less than 1. Arrays and OC are extremely fast at finding an object for an integer key but you wouldn't want to use them for a sparsely populated collection because a slot is allocated for every possible key. Use a Dictionary unless you are certain that an Array meets your needs.

 

A Dictionary allows "any" kind of object (except nil) to be used as a key. An object that is used as the key of a dictionary is first sent #hash to determine where to start looking for an equal key, keys are then compared with #= equality tests to find a match. If you use your own objects as keys then you sometimes want to define what it means for two of those objects to be considered equal. Equal objects need to return true from #=, but what most people new to Smalltalk miss is that those equal objects need to also answer an equal number from #hash so that hashed collections (like Dictionary and Set for example) start looking for a match at the correct index position. Kernel objects like integer and point (the examples you gave) already define both #= and #hash. Most people use common objects like strings and integers for dictionary keys instead of defining what it means for two of their domain objects to be considered equal.

 

An interval is an object that is similar to the "(1 - 16)...or 1@1" object you seemed to be considering as a key. I suspect you are thinking of using a dictionary different from how it is designed to operate. This demonstrates that key like that is one object and not many:

 

Dictionary new

            at: (1 to: 16) put: #findme;

            at: (1 to: 16) ifAbsent: [#nothing]

#findme

 

Dictionary new

            at: (1 to: 1000) put: #findme;

            at: (1 to: 16) ifAbsent: [#nothing]

#nothing

 

Here are examples of filling with a range of keys:

 

| index |

index := OrderedCollection new.

1 to: 16 do: [:i | index at: i put: #findme].

index at: 15

 

or:

 

| index |

index := Dictionary new.

1 to: 16 do: [:i | index at: i put: #findme ].

index at: 15

 

Your original question seemed to be more about how to get random numbers within a range. This is an example that uses a block to get 1000 random integers between 33 and 64:

 

| range randomStream aBlock |

randomStream := Random new.

range := 33 to: 64.

aBlock := [(randomStream next * range size + range first) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

Or, now reading randomly from values in the range interval:

 

| range randomStream aBlock |

randomStream := Random new.

range := 33 to: 64.

aBlock := [range at: 1 + (randomStream next * range size) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

And now an example of randomly selecting from a collection of specific values:

 

| range randomStream aBlock |

randomStream := Random new.

range := #(43 61 89 127 181 257 367 521 739 1049 1481 2099).

aBlock := [range at: 1 + (randomStream next * range size) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

All your "power of 2" numbers can be in the 'range' collection above. You could randomly select any object from a collection in the same way. Figuring out how the examples work would be a good exercise. Not many programming languages allow you to use block closures like this.

 

Paul Baumann

 

Correct, that was my original question.
What I try to figure out is the next step. How can I represent the 4 x 4 grid with on the two positions choosen by the random function  a "2" and all the others empty.

I thought I could use the position of the grid but maybe I can better use the numbers 1 - 16.

I will study your examples so I can learn more about Collectiions and how they work.

Roelof


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Paul Baumann schreef op 11-4-2014 23:57:

Hi Roelof,

 

A little more detail...

 

>> I have read the document and I doubt between a Directonary or a Array.
>> I will test if the number ( 1- 16) can be a key for a Directonary or that I still can use something like "1@1" as key.

 

Array can only be accessed with integer "keys", and only within the size allocated. Arrays don't grow in VisualWorks and most other Smalltalk dialects, so if you need growth then use an OrderedCollection instead of an Array. Both OC and Array will error if you attempt to access a position greater than the size allocated or less than 1. Arrays and OC are extremely fast at finding an object for an integer key but you wouldn't want to use them for a sparsely populated collection because a slot is allocated for every possible key. Use a Dictionary unless you are certain that an Array meets your needs.

 

A Dictionary allows "any" kind of object (except nil) to be used as a key. An object that is used as the key of a dictionary is first sent #hash to determine where to start looking for an equal key, keys are then compared with #= equality tests to find a match. If you use your own objects as keys then you sometimes want to define what it means for two of those objects to be considered equal. Equal objects need to return true from #=, but what most people new to Smalltalk miss is that those equal objects need to also answer an equal number from #hash so that hashed collections (like Dictionary and Set for example) start looking for a match at the correct index position. Kernel objects like integer and point (the examples you gave) already define both #= and #hash. Most people use common objects like strings and integers for dictionary keys instead of defining what it means for two of their domain objects to be considered equal.

 

An interval is an object that is similar to the "(1 - 16)...or 1@1" object you seemed to be considering as a key. I suspect you are thinking of using a dictionary different from how it is designed to operate. This demonstrates that key like that is one object and not many:

 

Dictionary new

            at: (1 to: 16) put: #findme;

            at: (1 to: 16) ifAbsent: [#nothing]

#findme

 

Dictionary new

            at: (1 to: 1000) put: #findme;

            at: (1 to: 16) ifAbsent: [#nothing]

#nothing

 

Here are examples of filling with a range of keys:

 

| index |

index := OrderedCollection new.

1 to: 16 do: [:i | index at: i put: #findme].

index at: 15

 

or:

 

| index |

index := Dictionary new.

1 to: 16 do: [:i | index at: i put: #findme ].

index at: 15

 

Your original question seemed to be more about how to get random numbers within a range. This is an example that uses a block to get 1000 random integers between 33 and 64:

 

| range randomStream aBlock |

randomStream := Random new.

range := 33 to: 64.

aBlock := [(randomStream next * range size + range first) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

Or, now reading randomly from values in the range interval:

 

| range randomStream aBlock |

randomStream := Random new.

range := 33 to: 64.

aBlock := [range at: 1 + (randomStream next * range size) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

And now an example of randomly selecting from a collection of specific values:

 

| range randomStream aBlock |

randomStream := Random new.

range := #(43 61 89 127 181 257 367 521 739 1049 1481 2099).

aBlock := [range at: 1 + (randomStream next * range size) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

All your "power of 2" numbers can be in the 'range' collection above. You could randomly select any object from a collection in the same way. Figuring out how the examples work would be a good exercise. Not many programming languages allow you to use block closures like this.

 

Paul Baumann

 

Correct, that was my original question.
What I try to figure out is the next step. How can I represent the 4 x 4 grid with on the two positions choosen by the random function  a "2" and all the others empty.

I thought I could use the position of the grid but maybe I can better use the numbers 1 - 16.

I will study your examples so I can learn more about Collectiions and how they work.

Roelof

I see one little problem. With this script it is possible that the same number gets "choosen" two times.
So I have to use a set I think to solve that one.

Roelof



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Roelof Wobben schreef op 12-4-2014 8:40:

Paul Baumann schreef op 11-4-2014 23:57:

Hi Roelof,

 

A little more detail...

 

>> I have read the document and I doubt between a Directonary or a Array.
>> I will test if the number ( 1- 16) can be a key for a Directonary or that I still can use something like "1@1" as key.

 

Array can only be accessed with integer "keys", and only within the size allocated. Arrays don't grow in VisualWorks and most other Smalltalk dialects, so if you need growth then use an OrderedCollection instead of an Array. Both OC and Array will error if you attempt to access a position greater than the size allocated or less than 1. Arrays and OC are extremely fast at finding an object for an integer key but you wouldn't want to use them for a sparsely populated collection because a slot is allocated for every possible key. Use a Dictionary unless you are certain that an Array meets your needs.

 

A Dictionary allows "any" kind of object (except nil) to be used as a key. An object that is used as the key of a dictionary is first sent #hash to determine where to start looking for an equal key, keys are then compared with #= equality tests to find a match. If you use your own objects as keys then you sometimes want to define what it means for two of those objects to be considered equal. Equal objects need to return true from #=, but what most people new to Smalltalk miss is that those equal objects need to also answer an equal number from #hash so that hashed collections (like Dictionary and Set for example) start looking for a match at the correct index position. Kernel objects like integer and point (the examples you gave) already define both #= and #hash. Most people use common objects like strings and integers for dictionary keys instead of defining what it means for two of their domain objects to be considered equal.

 

An interval is an object that is similar to the "(1 - 16)...or 1@1" object you seemed to be considering as a key. I suspect you are thinking of using a dictionary different from how it is designed to operate. This demonstrates that key like that is one object and not many:

 

Dictionary new

            at: (1 to: 16) put: #findme;

            at: (1 to: 16) ifAbsent: [#nothing]

#findme

 

Dictionary new

            at: (1 to: 1000) put: #findme;

            at: (1 to: 16) ifAbsent: [#nothing]

#nothing

 

Here are examples of filling with a range of keys:

 

| index |

index := OrderedCollection new.

1 to: 16 do: [:i | index at: i put: #findme].

index at: 15

 

or:

 

| index |

index := Dictionary new.

1 to: 16 do: [:i | index at: i put: #findme ].

index at: 15

 

Your original question seemed to be more about how to get random numbers within a range. This is an example that uses a block to get 1000 random integers between 33 and 64:

 

| range randomStream aBlock |

randomStream := Random new.

range := 33 to: 64.

aBlock := [(randomStream next * range size + range first) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

Or, now reading randomly from values in the range interval:

 

| range randomStream aBlock |

randomStream := Random new.

range := 33 to: 64.

aBlock := [range at: 1 + (randomStream next * range size) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

And now an example of randomly selecting from a collection of specific values:

 

| range randomStream aBlock |

randomStream := Random new.

range := #(43 61 89 127 181 257 367 521 739 1049 1481 2099).

aBlock := [range at: 1 + (randomStream next * range size) asInteger].

(1 to: 1000) collect: [:i | aBlock value ].

 

All your "power of 2" numbers can be in the 'range' collection above. You could randomly select any object from a collection in the same way. Figuring out how the examples work would be a good exercise. Not many programming languages allow you to use block closures like this.

 

Paul Baumann

 

Correct, that was my original question.
What I try to figure out is the next step. How can I represent the 4 x 4 grid with on the two positions choosen by the random function  a "2" and all the others empty.

I thought I could use the position of the grid but maybe I can better use the numbers 1 - 16.

I will study your examples so I can learn more about Collectiions and how they work.

Roelof

I see one little problem. With this script it is possible that the same number gets "choosen" two times.
So I have to use a set I think to solve that one.

Roelof

yep, If I make ablock a set everything works as expected.



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>>From: Roelof Wobben

>>What I try to figure out is the next step. How can I represent the 4 x 4 grid with on the two positions choosen by the random function

>>  a "2" and all the others empty.

 

Not sure what you mean by (a "2" and all the others empty), but this is one way to do the first part using a 2D literal array:

| fourByFour randomStream |

fourByFour := #(

            (1 2 3 4)

            (5 6 7 8)

            (9 10 11 12)

            (13 14 15 16)

).

randomStream := Random new.

(1 to: 100) collect: [:i |

            | pos |

            pos := ((randomStream next * 4) asInteger + 1) @ ((randomStream next * 4) asInteger + 1).

            pos -> ((fourByFour at: pos y) at: pos x).

].

 

>>I thought I could use the position of the grid but maybe I can better use the numbers 1 - 16.

This shows converting the 4x4 grid to a dictionary with points as keys, and then randomly gets 100 of them:

 

| fourByFour dict randomStream |

fourByFour := #(

            (1 2 3 4)

            (5 6 7 8)

            (9 10 11 12)

            (13 14 15 16)

).

dict := Dictionary new.

fourByFour doWithIndex: [:yArray :y |

            yArray doWithIndex: [:value :x |

                        dict at: (x @ y) put: value

            ].

].

randomStream := Random new.

(1 to: 100) collect: [:i |

            | pos |

            pos := ((randomStream next * 4) asInteger + 1) @ ((randomStream next * 4) asInteger + 1).

            dict associationAt: pos.

].

 

More efficient access would be from flattening the 2D grid to a 1D sequenceable collection and using a single random (no point creation) for access:

 

| fourByFour all randomStream |

randomStream := Random new.

fourByFour := #(

                (1 2 3 4)

                (5 6 7 8)

                (9 10 11 12)

                (13 14 15 16)

).

all := OrderedCollection new.

fourByFour doWithIndex: [:yArray :y |

                yArray doWithIndex: [:value :x |

                                all add: (x @ y) -> value

                ].

].

(1 to: 100) collect: [:i |

                | pos |

                pos := (randomStream next * all size) asInteger + 1.

                all at: pos.

].

 

Paul Baumann

 

 

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Thanks,

What Im looking for is it.
I need a 4 X 4 grid where 2 tiles have a value of 2.
The rest can be empty or 0
The two tiles are random choosen out of all the tiles.

Roelof


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