Repeat function in python similar to R

Question

The question is: Is there a repeat function in python similar to R rep function? R have a powerful rep function as follows:

rep(x, times = 1, length.out = NA, each = 1)

• x: a vector

• times: an integer-valued vector giving the (non-negative) number of times to repeat each element if of length length(x), or to repeat the whole vector if of length 1. Negative or NA values are an error. A double vector is accepted, other inputs being coerced to an integer or double vector.

• length.out: non-negative integer. The desired length of the output vector. Other inputs will be coerced to a double vector and the first element taken. Ignored if NA or invalid.

• each: non-negative integer. Each element of x is repeated each times. Other inputs will be coerced to an integer or double vector and the first element taken. Treated as 1 if NA or invalid.

Some examples are as follows:

R code
> letters
 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" "v"
[23] "w" "x" "y" "z"
#Example 1
> rep(letters[1:3],times=c(1,2,4))
[1] "a" "b" "b" "c" "c" "c" "c"
#Example 2
> rep(letters[1:3],each=2,len=15)
 [1] "a" "a" "b" "b" "c" "c" "a" "a" "b" "b" "c" "c" "a" "a" "b"
#repeat a:c each element 2 until length be 15
#Example 3
> rep(letters[1:3],each=3,times=2)
 [1] "a" "a" "a" "b" "b" "b" "c" "c" "c" "a" "a" "a" "b" "b" "b" "c" "c" "c"
#repeat a:c each element 3  and repeat this 2 times
#Example 4
> rep(letters[c(TRUE,FALSE)],each=2)
 [1] "a" "a" "c" "c" "e" "e" "g" "g" "i" "i" "k" "k" "m" "m" "o" "o" "q" "q" "s" "s" "u" "u"
[23] "w" "w" "y" "y"
#Example 5
> rep(letters[c(TRUE,FALSE,TRUE,FALSE,FALSE)],each=2)
 [1] "a" "a" "c" "c" "f" "f" "h" "h" "k" "k" "m" "m" "p" "p" "r" "r" "u" "u" "w" "w" "z" "z"
#Example 6
> rep(letters[c(TRUE,FALSE,TRUE,FALSE,FALSE)],each=2,len=25)
[1] "a" "a" "c" "c" "f" "f" "h" "h" "k" "k" "m" "m" "p" "p" "r" "r" "u" "u" "w" "w" "z" "z"
[23] "a" "a" "c"

In python I just found functions that repeat each element of a array, that is, repeat elements of an array 4 times.

Python
import numpy as np
import string
letters =string.ascii_lowercase
letters =list(letters)
print(np.repeat(letters, 2))
['a' 'a' 'b' 'b' 'c' 'c' 'd' 'd' 'e' 'e' 'f' 'f' 'g' 'g' 'h' 'h' 'i' 'i'
 'j' 'j' 'k' 'k' 'l' 'l' 'm' 'm' 'n' 'n' 'o' 'o' 'p' 'p' 'q' 'q' 'r' 'r'
 's' 's' 't' 't' 'u' 'u' 'v' 'v' 'w' 'w' 'x' 'x' 'y' 'y' 'z' 'z']
 
print(np.repeat(['a','b'], [1,2]))
['a' 'b' 'b']

Is it possible to use numpy.repeat like rep function in R(see example 4,5,6)? if not? Is there a function that does the same as R's rep? If not how to create one?

Answer 1

Its not quite clear what you want to achieve. You can use slicing to get an equivalent output in numpy like Example 4, or you can use indexing with a mask to get your desired results (Example 5). There is not an exact equivalent function in python.

# Example 4
import numpy as np
import string
letters =string.ascii_lowercase
letters =list(letters)

print(np.repeat(letters[::2],2))

['a' 'a' 'c' 'c' 'e' 'e' 'g' 'g' 'i' 'i' 'k' 'k' 'm' 'm' 'o' 'o' 'q' 'q'
 's' 's' 'u' 'u' 'w' 'w' 'y' 'y']

# Example 5
import numpy as np
import string
letters =string.ascii_lowercase  
letters = np.array(list(letters))

indicies = [(0,2,5,7,10,12,15,17,20,22,25)]

print(np.repeat(letters[indicies],2))

['a' 'a' 'c' 'c' 'f' 'f' 'h' 'h' 'k' 'k' 'm' 'm' 'p' 'p' 'r' 'r' 'u' 'u'
 'w' 'w' 'z' 'z']