# Vocabulary/minusdot

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`-. y`Not

Rank 0 *-- operates on individual atoms of y, producing a result of the same shape --*
WHY IS THIS IMPORTANT?

Equivalent to `1 - y` .

- for Boolean
`y`(`0`or`1`) -- (`-.y`) is the Boolean function*Not*.

- for
`y`as a*probability*(in the*closed interval*[0,1]) -- (`-.y`) is the*complementary*probability.

-. 0 1 NB. Boolean "Not" 1 0 -. 0.25 0.3333333 0.8 NB. Complements of the probabilities ("1-p" versus "p") 0.75 0.6666667 0.2

### Common Uses

-.'encephalogram' e. 'aeiouAEIOU' NB. Which characters are not vowels? 0 1 1 0 1 1 0 1 0 1 1 0 1 str#~-.str e. 'aeiouAEIOU' [ str=. 'encephalogram' NB. Show only non-vowels ncphlgrm

This latter example is more elegantly accomplished using the dyadic form - see below.

2. Reverse the meaning of the trigger of an `if.`-statement

if. aa -.@-: bb do. ... NB. If "aa" is not equivalent to "bb" ...

Get in the habit of writing `aa -.@-: bb` rather than `-. aa -: bb` - it's faster.

3. Calculate the probability of event not happening, given the probability of it happening

%6 NB. Probability of six turning up on roll of fair 6-sided die 0.16666667 -.%6 NB. Probability of six not turning up on roll of same... 0.83333333 (-.%6)^4 NB. Probability of no sixes turning up on roll of 4 dice 0.48225309 -.(-.%6)^4 NB. Probability of at least one six turning up on roll of 4 dice 0.51774691

### Related Primitives

Or (`x +. y`),
Not-Or (`x +: y`),
LCM (And) (`x *. y`),
Not-And (`x *: y`),
Boolean Functions (`m b.`)

### Use These Combinations

Combinations using `-. y` that have exceptionally good performance include:

**What it does****Type;**

**Precisions;**

Ranks**Syntax****Variants;**

**Restrictions****Benefits;**

**Bug Warnings**Not-match `x -.@-: y``@:`in place of`@`Use this form for not-match. Supported as a primitive by `(-.@-:)"n`

`x -. y`Less

Rank Infinity *-- operates on x and y as a whole, by items of x --*
WHY IS THIS IMPORTANT?

When `x` and `y` are lists, `x -. y` is all the atoms of `x` that are **not** in `y`, preserving the original order in `x`.
(`A-.B`) has the following *Venn diagram*

### Common Uses

1. Remove all vowels from a string

'encephalogram' -. 'aeiouAEIOU' ncphlgrm

2. Read a text file but exclude all `CR` (carriage-return characters)

fl=. (fread 'file.txt') -. CR fl=. CR-.~fread 'file.txt' NB. alternative form

### More Information

1. `x -. y` used tolerant comparison on numeric values. Use `-.!.0` to force exact comparison.

2. `x -. y` is a member of the i.-family.

3. If `x` is an atom then it is turned into a 1-element list before being processed. The result is always an array.

4. The internal rank of `x -. y` uses items whose rank is the rank of items of `x`.
Calling the rank of an item of `x` *rix*, any item of `x` that matches an *rix*-cell of `y` is deleted.

(i. 9) -. 2 2 $ 1 3 5 6 NB. Items of x are atoms 0 2 4 7 8 (i. 3 4) -. 0 1 2 3 NB. Items of x are lists 4 5 6 7 8 9 10 11

5. If `x` and `y` are of different types, or if their items couldn't possibly match because of differing shapes,
no error is signaled: each search simply fails to match, and no items are removed.

### Use These Combinations

Combinations using `x -. y` that have exceptionally good performance include:

**What it does****Type;**

**Precisions;**

Ranks**Syntax****Variants;**

**Restrictions****Benefits;**

**Bug Warnings**Remove items of `m`from`y``-.&m y``-.!.0`for exact comparison**Bug warning:**removes items of`m`from`y`, rather than removing items of`y`that match cells of`m`. This may lead to error if it attempts to delete part of an item of`y`.