shift() and unshift() on the other hand I always had trouble with. One of them adds a new element to the front of the array and the other removes and returns the 1st element. But which is which? I can google the answer but would be nice if I didn't have to google. And worse, sometimes I got confused between the two and used shift() where unshift() should have been used => Error,, stack overflow!
So I googled for "Mnemonics for shift() and unshift()", and found an entry on Stack Overflow. But that question was "Closed because the answers are opinion-based". I looked at the answers available but none of them struck me as particularly memorable.
Now after years of struggling with this confusion I think I've come up with a mnemonic I can live with:
Word "shift" is shorter than the word "unshift". Therefore shift() makes the array shorter.
Word "unshift" is longer than the word "shift". Therefore unshift() makes the array longer.
I know it doesn't really explain it, but it is a rule I can remember. I would appreciate hearing how anybody else remembers when to use shift() and when to use unshift().
Neither of those has unshift, but you can infer its meaning from knowing about shift.
I also think push and pop aren’t good names. append, respectively removelast are way better.
But I don't want to do that. Why because: It is not a good practice to modify JavaScript built-in prototypes. If that was the recommended practice then someone else's code might do a similar thing, but assign some other function to it. Whoever writes it last overrides any previous definition.
I don't use someone else's code. I use my code. But I may be the minority.
Use a namespace, then.
fifo : first in, first out (stack of plates) -- taking from front/top, adding to front/top. -- shift on "1"/push; unshift off "0"/pop. start with at least one shift/push. ideally equal number of unshifts/pops by end of task to clear the stack array.
"prepend" is used to describe adding something at the beginning of a sequence.
Good old "cons" has the specific technical meaning of placing data at the lowest address of a sequential memory structure...and it is shorter than "append" and "prepend."
IF JavaScript had them as built-ins it would be great, then I wouldn't need to look for mnemonics for shift() and unshift() :-)
But, I googled "prepend" and guess what: google replied
"Although it sounds correct, prepend is not an English word. It was created to sound like the opposite of "append," which means to add to the end. The correct English word is "prefix".
A slight problem with that is that "prefix" is more often used as a noun than as a verb, I think.
Anyway, "cons" is a better term in technical contexts.
Shift on an array similarly shifts an element off the array. Unshift puts an element back on the array.
Maybe more graphically: I you shift books on a shelf, the outermost book may fall off the shelf. To put it back on, you first need to “unshift” the books.
How I actually remember it is from Perl, where shift is commonly used to process the next argument from the argument array. And you rarely unshift.
Also "unshift" does not imply in any way that you are adding a new book to your shelf, and to which side of it.
The direction is simple to remember: It’s the opposite from push/pop. I thought this wasn’t your issue. But there is another way to remember, in case you forget what direction push/pop is: Removing an item from the end of an array doesn’t require shifting (moving) the remaining elements (their indices remain the same). Removing an element from the front, however, requires shifting the elements (their indices do change). Therefore shift/unshift are the operations at the front of the array, and push/pop are the ones at the back.
The bookshelf analogy relies on "shift" being more common than "unshift" (otherwise the operations would have been named the other way around), and that shifting your books on a shelf is more common than the case where one book falls off the shelf and you have to put it back up ("unshift").
The reason using both shift and unshift is less common, as opposed to push and pop, is again due to efficiency considerations, since the latter don’t require shifting all elements. If you want to use the array as a LIFO stack, you use push and pop. If you want to use it as a FIFO queue, you use push and shift. Unshift is usually only used in more exceptional cases.
“Unshift”, like “push”, contains the letter “u”.
I remember the same way I remember anything else — by memorizing.
In British English “shift” means “move,” so shifting something off an array means moving it (into a variable). Un- as a prefix indicates negation or reversing in English. So you just need to remember what shift does, and unshift does the opposite, as indicated by the word.
Indeed, part of my motivation for writing this was to remember it. I have spent too much time thinking about what shift() vs. unshift() do.
The other part was that I wanted to know how others figure out when to use shift() and when to use unshift(). Thanks for everybody for your suggestions.
> Word "unshift" is longer than the word "shift". Therefore unshift() makes the array longer.
This is quite useful as I too couldn't remember which is which. Thanks for sharing!
html < is open block, html > is close block.
< and << are logical shift left for array of bits.
> and >> are logical shift right for array of bits.
Looking at only 'logical value of 1'. Have to open/shift left before unopen/shift right to make thing correct. aka init variable to 0; shift left/push gives 1; shift right/removes aka pops the 1.
html < pushes/shifts all the commands onto stack.
html > pops all the commands todo off of the stack until reach < aka end of stack marker.
- C also has functions called getc() and ungetc(), and they're analogous.
- "Doing" and "undoing" are actually the same in some sense: doing causes information loss, undoing causes information gain.
especially the internals of array sort method.
this is how it works in all languages
same concept as << (bit wise left shift)