How to delete array

Ruby
1

Problem

consider an array

a = [1,4,6,7,9,8]

I want to delete the array value w.r.t index

e.g i want to delte 0,4,6 element in one go

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

But the problem is that i dont know how much element will be populated
in my array every time the program runs and the index value will also
change.

So i need to dynamically pass the index value and this should delete the
values pertaining to the index

2

Surjit N. wrote:

a = [1,4,6,7,9,8]

I want to delete the array value w.r.t index

e.g i want to delte 0,4,6 element in one go

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

But the problem is that i dont know how much element will be populated
in my array every time the program runs and the index value will also
change.

So i need to dynamically pass the index value and this should delete the
values pertaining to the index

You can’t delete by index if you don’t have an index, so I assume your
program will have the index in some form or another. Perhaps in a
variable?

a.delete(some_index) # where some_index contains an integer

If you post more of your program we’ll be better able to help you.

3

Surjit N. wrote:

Problem

consider an array

a = [1,4,6,7,9,8]

I want to delete the array value w.r.t index

e.g i want to delte 0,4,6 element in one go

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

But the problem is that i dont know how much element will be populated
in my array every time the program runs and the index value will also
change.

So i need to dynamically pass the index value and this should delete the
values pertaining to the index

you could try something like…

a.each_with_index do |item, index|
a.delete_at(index) if item.eql?(something)
end

~Jeremy

4

On Nov 7, 2007 10:02 PM, Surjit N. [email protected]
wrote:

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

But the problem is that i dont know how much element will be populated
in my array every time the program runs and the index value will also
change.

If you really want to delete a few indexes you can build a new array:
b = []
a.each_with_index {|e, i| b<< e if [0, 4, 6].include?(i)}
a=b

5

If i have an array

a = [1,2,3,4]

The default index of 1 is 0

so we use a.delete_at(0) to delete 1

See my Q’s again

6

Jeremy W. wrote:

Surjit N. wrote:

Problem

consider an array

a = [1,4,6,7,9,8]

I want to delete the array value w.r.t index

e.g i want to delte 0,4,6 element in one go

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

But the problem is that i dont know how much element will be populated
in my array every time the program runs and the index value will also
change.

So i need to dynamically pass the index value and this should delete the
values pertaining to the index

you could try something like…

a.each_with_index do |item, index|
a.delete_at(index) if item.eql?(something)
end

~Jeremy

I think you want Array#delete_if.

a.delete_if {|v| v == 1}

deletes all entries in a that are 1.

7

My business logic doesn’t help me find which values i have to delete but
i will know what are the indexes i have to delete.

8

On Nov 7, 2007 10:02 PM, Surjit N. [email protected]
wrote:

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

Mostly when I have a problem like this, I find that the indexes I want
to
delete are a list generated by some property of the elements. ie.
perhaps
you want to delete indexes 0, 4, 6 because the elements at those indexes
are
(say) larger than three.

In that case, there’s a much cleaner way:
a.reject!{|e| e > 3}

If you can say how you calculate that list of indexes to delete, we may
be
able to help better.

Les

9

Surjit N. wrote:

My business logic doesn’t help me find which values i have to delete but
i will know what are the indexes i have to delete.

Actually i have collected the indexes i have to delete in an array

e.g

Array1 = [1,2,3,4,7,4]

indexes to be delted is collected in an array del=[1,3] …i.e i should
delete 2 and 4 values

i tried using

Array1.delete_at(del[])

but this doesn’t work

10

On Nov 7, 2007, at 1:40 PM, Surjit N. wrote:

indexes to be delted is collected in an array del=[1,3] …i.e i should
delete 2 and 4 values

i tried using

Array1.delete_at(del[])

Array1 = [1,2,3,4,7,4]
del = [1,3]
del.sort.reverse.each {|index| Array1.delete_at(index)}

You need to do the sort.reverse trick so that you don’t change the
size of Array1 and then try to delete one of the larger indicies.
WIth sort.reverse, you’ll always be deleting the largest index first.

I know you can pass a block to sort to reverse the order, but
sort.reverse is a little clearer (although less efficient).

Blessings,
TwP

11

F5

12

On Nov 7, 2007 3:00 PM, Tim P. [email protected] wrote:

Array1 = [1,2,3,4,7,4]

Blessings,
TwP

This is good unless they have an index in del that happens outside of
the size of the array.

If they can guarantee a value that should never occur in the original,
a better way (though more wordy) might be…

v = value_that_never_occurs = nil
array1 = 1 ,2 ,3 ,4 ,7 ,4
indices = 1, 3
indices.each { |i| array1[i] = v }
array1.delete(nil)
p array1

just another thought,
Todd

13

On Nov 7, 2007, at 1:40 PM, Surjit N. wrote:

cfp:~ > cat a.rb
array = 1, 2, 3, 4, 7, 4

index = 1, 3
i = -1
array.delete_if{ index.delete(i+=1) }

p array #=> [1, 3, 7, 4]

index = -2, -1
i = -(array.size + 1)
array.delete_if{ index.delete(i+=1) }

p array #=> [1, 3]

cfp:~ > ruby a.rb
[1, 3, 7, 4]
[1, 3]

this approach avoids any sorting or extra copying and also does the
deletion in one pass.

regards.

a @ http://codeforpeople.com/

14

On Nov 7, 2007 10:05 PM, Todd B. [email protected] wrote:

On Nov 7, 2007 9:47 PM, ara.t.howard [email protected] wrote:

has nothing to do with the Array’s ordering, so I was a little
surprised at this assumption.

Todd

Nevermind that. I can see how you might want to consider position in
a condition (maybe state machine stuff or whatever). #delete_if is
after all an Array method, which is the only set of objects that
require a linear order. Sorry for noise now.

Todd

15

On Nov 7, 2007 9:47 PM, ara.t.howard [email protected] wrote:

array.delete_if{ index.delete(i+=1) }
This is excellent! Only, what if your underlying implementation does
not traverse an array in order with #delete_if ? As it turns out, it
does, but would it have to? I see #delete_if as a conditional that
has nothing to do with the Array’s ordering, so I was a little
surprised at this assumption.

Todd

16

On Nov 7, 2007, at 9:11 PM, Todd B. wrote:

Nevermind that. I can see how you might want to consider position in
a condition (maybe state machine stuff or whatever). #delete_if is
after all an Array method, which is the only set of objects that
require a linear order. Sorry for noise now.

no that’s really a valid concern i think - happens to be that
#delete_if is defined in terms of #each (from Enumerable) so i know
it’s in order but once indeed needs to assume/know that for it to work.

cheers.

a @ http://codeforpeople.com/

17

On Behalf Of Surjit N.

Array1 = [1,2,3,4,7,4]

indexes to be delted is collected in an array del=[1,3] …i.e

i should

delete 2 and 4 values

i tried using

Array1.delete_at(del[])

but this doesn’t work

loop thru your indexes to the array, ie,

array = [1,2,3,4,7,4]
=> [1, 2, 3, 4, 7, 4]
del=[1,3]
=> [1, 3]
del.each{|i| array.delete_at(i)}
=> [1, 3]
array
=> [1, 3, 4, 4]

or you can then create your own fancy delete_at method

class Array
def delete_atx(d)
d.each{|i| self.delete_at(i)}
end
end
=> nil
array = [1,2,3,4,7,4]
=> [1, 2, 3, 4, 7, 4]
del=[1,3]
=> [1, 3]
array.delete_atx del
=> [1, 3]
array
=> [1, 3, 4, 4]

kind regards -botp

18

On 07.11.2007 21:02, Surjit N. wrote:

I can use the command
a.delete_at(0)
a.delete_at(4)
a.delete_at(6)

But the problem is that i dont know how much element will be populated
in my array every time the program runs and the index value will also
change.

So i need to dynamically pass the index value and this should delete the
values pertaining to the index

I am surprised nobody mentioned slice - just apply indexes in decreasing
order:

irb(main):012:0> a = [1,4,6,7,9,8]
=> [1, 4, 6, 7, 9, 8]
irb(main):013:0> a.slice! 2,1
=> [6]
irb(main):014:0> a
=> [1, 4, 7, 9, 8]
irb(main):015:0> a.slice! 1,1
=> [4]
irb(main):016:0> a
=> [1, 7, 9, 8]

Kind regards

robert

19

On Nov 8, 2007 5:40 AM, Surjit N. [email protected]
wrote:

but this doesn’t work

Array1 = [1,2,3,4,7,4]
del = [1,3]
keep = []

(0…Array1.length).each do |x|
keep << Array1[x] unless del.include?(x)
end

p keep #> [1, 3, 7, 4]

Harry

20

I got it working now…Thanks a lot everyone for all the suggestions…