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Ruby Copy Array Example
Copy arrays with the slice operator. Changes to a copied array do not affect the original one.Copy array. An array is stored in a region of memory. When we modify it, we modify that region of memory. Two array variables can point to the same region. We can copy an array, with slice syntax, to create separate arrays.Array
Example. First, this program slices an array with the square-bracket syntax. It specifies a slice on "values" from 0 to values.length. This is a total-array slice. After the slice, "values" and "copy" point to separate memory regions.
Note: We test that our arrays are separate. We modify the copied array, and the original array is not changed.
Ruby program that copies array
# Create an array.
values = ["cat", "dog", "mouse"]
print "VALUES: ", values, "\n"
# Copy the array using a total-array slice.
# ... Modify the new array.
copy = values[0 .. values.length]
copy[0] = "snail"
print "COPY: ", copy, "\n"
# The original array was not modified.
print "VALUES: ", values, "\n"
Output
VALUES: ["cat", "dog", "mouse"]
COPY: ["snail", "dog", "mouse"]
VALUES: ["cat", "dog", "mouse"]
Example 2. This example is similar, but has one difference. It specifies the length of the slice with a final index of negative one. This means "the last index." This is the shortest syntax form.
Tip: This syntax form is not better (or worse) than the previous one. It comes down to what syntax form you prefer.
Ruby program that copies array with negative one
values = [1, 10, 100]
# Copy the array with a different syntax.
copy = values[0 .. -1]
copy[0] = 1000
# Display the arrays.
print values, "\n"
print copy, "\n"
Output
[1, 10, 100]
[1000, 10, 100]
Slice. The slice method is an alias for the square-bracket slicing syntax. So calling slice with the same arguments as above yields an equivalent result. Please be sure to use two dots to separate arguments, not a comma.
Opinion: For an experienced developer using Ruby, a total-array slice is easy to understand.
Ruby program that uses slice, copies array
values = [8, 9, 10]
# Use slice method to copy array.
copy = values.slice(0 .. -1)
copy[0] = 5
# Display two arrays.
print values, "\n"
print copy, "\n"
Output
[8, 9, 10]
[5, 9, 10]
Summary. When developing programs, an array copy is sometimes needed. If you do not copy an array, the original array will be modified. And once modified, you might not be able to retrieve the original values.
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