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https://github.com/gdemin/comprehenr
List comprehensions in R
https://github.com/gdemin/comprehenr
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List comprehensions in R
- Host: GitHub
- URL: https://github.com/gdemin/comprehenr
- Owner: gdemin
- Created: 2019-02-17T15:25:41.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2023-05-06T23:43:14.000Z (over 1 year ago)
- Last Synced: 2024-08-03T22:20:03.947Z (4 months ago)
- Language: HTML
- Homepage:
- Size: 43 KB
- Stars: 20
- Watchers: 3
- Forks: 1
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
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README
# List comprehensions in R
[](https://cran.r-project.org/package=comprehenr)
[](https://cran.rstudio.com/web/packages/comprehenr/index.html)
[](https://cran.rstudio.com/web/packages/comprehenr/index.html)
[](https://codecov.io/github/gdemin/comprehenr?branch=master)
Package provides Python-style list comprehensions for R. List comprehension
expressions use usual loops (`for`, `while` and `repeat`) and usual `if` as
list producers. Syntax is very similar to Python. The difference is that
returned value should be at the end of the loop body.
There are three main functions:
- `to_list` converts usual R loops expressions to list producers. Expression should be started with `for`, `while` or `repeat`. You can iterate over multiple lists if you provide several loop variables in backticks. See examples.
- `to_vec` is the same as `to_list` but return vector. See examples.
- `alter` return the same type as its argument but with modified elements. It is useful for altering existing data.frames or lists. See examples.
Rather unpractical example - squares of even numbers:
```R
library(comprehenr)
to_vec(for(i in 1:10) if(i %% 2==0) i*i)
```
Pythagorean triples:
```R
to_list(for (x in 1:20) for (y in x:20) for (z in y:20) if (x^2 + y^2 == z^2) c(x, y, z))
```
More examples:
```R
colours = c("red", "green", "yellow", "blue")
things = c("house", "car", "tree")
to_vec(for(x in colours) for(y in things) paste(x, y))
# prime numbers
noprimes = to_vec(for (i in 2:7) for (j in seq(i*2, 99, i)) j)
primes = to_vec(for (x in 2:99) if(!x %in% noprimes) x)
primes
```
You can iterate over multiple lists if you provide several loop variables in backticks:
```R
to_vec(for(`i, j` in numerate(letters)) if(i %% 2==0) paste(i, j))
set.seed(123)
rand_sequence = runif(20)
# gives only locally increasing values
to_vec(for(`i, j` in lag_list(rand_sequence)) if(j>i) j)
```
`alter` examples:
```R
data(iris)
# scale numeric variables
res = alter(for(i in iris) if(is.numeric(i)) scale(i))
str(res)
# convert factors to characters
res = alter(for(i in iris) if(is.factor(i)) as.character(i))
str(res)
# drop factors
res = alter(for(i in iris) if(is.factor(i)) exclude())
str(res)
# 'data' argument example
# specify which columns to map with a numeric vector of positions:
res = alter(
for(`i, value` in numerate(mtcars)) if(i %in% c(1, 4, 5)) as.character(value),
data = mtcars
)
str(res)
# or with a vector of names:
res = alter(
for(`name, value` in mark(mtcars)) if(name %in% c("cyl", "am")) as.character(value),
data = mtcars
)
str(res)
```