## Uniq and basic set theory

October 25th, 2006 toydi Posted in sort, Text Manipulation, uniq | Hits: 39456 | 1 Comment »

Imagine that I have two files:

`aquatic`

– contains a list of aquatic animals

```
starfish
whale
nemo
crab
dolphin
```

`mammal`

– contains a list of mammals

```
whale
RMS
batman
dolphin
scooby-doo
```

Given `aquatic`

and `mammal`

are two different sets, let’s use `sort`

and `uniq`

to play with a few basic set theory operations:

**Union** (* A U B* – members in either A or B )

*aquatic U mamal= {batman, crab, dolphin, nemo, RMS, scooby-doo, starfish, whale}*

`sort aquatic mammal | uniq `

**Intersection** ( *A âˆ© B* – members in both A and B )

*aquatic âˆ© mammal = {dolphin, whale}*

`sort aquatic mammal | uniq -d`

**Symmetric Difference** ( *A ^ B* – members in A or B but not both )

*aquatic ^ mammal = {batman, crab, nemo, RMS, scooby-doo, starfish}*

`sort aquatic mammal | uniq -u`

**Relative Complement** ( *A âˆ’ B* – members in A but not in B )

*aquatic âˆ’ mammal = {crab, nemo, starfish}*

`sort aquatic mammal | uniq -d | sort aquatic - | uniq -u`

`"sort aquatic mammal | uniq -d"`

performs an intersection:*aquatic âˆ© mammal = {dolphin, whale}*.`"sort aquatic - | uniq -u`

” performs a symmetric difference:*aquatic ^ {dolphin, whale} = {crab, nemo, starfish}.*

UPDATED**: **I found a piece of clean elegant codes to perform relative complement:

`sort aquatic mammal mammal | uniq -u`

.

**“sort -u”: a short-hand for “sort | uniq”**

`sort -u`

is equivalent to `sort | uniq`

to eliminate duplicated elements in a list. Therefore, you may replace:

`sort aquatic mammal | uniq`

with:

`sort -u aquatic mammal`

November 3rd, 2006 at 4:36 pm

[…] In a previous post, I used sort and uniq to emulate a few set theory operations. This time, I try to write them as functions: […]