How to Extract Multiples of a Number from a Vector

How to extract multiples of a number from a vector

For this you can use the modulo operator, i.e. %%. Take for example:

> 322%%8
[1] 2

which tells you that after dividing 322 by 8, 2 remains, i.e. 320 is exactly 40 times 8, leaving 2.

In you example we can use %% combined with subsetting to get the the multiples of 8. Remember that %% yields 0 for exact multiples of 8:

input = 1:1000
multiple_of_8 = (input %% 8) == 0
head(multiple_of_8)
[1] FALSE FALSE FALSE FALSE FALSE FALSE
length(multiple_of_8)
[1] 1000

also note that %% is a vectorized operation, i.e. of the left hand side is a vector, the result will also be a vector. The multiple_of_8 vector now contains 1000 logicals stating if that particular element of input is an exact multiple of 8. Using that logical vector to subset get's you the result you need:

input[multiple_of_8]
  [1]    8   16   24   32   40   48   56   64   72   80   88   96  104  112  120
 [16]  128  136  144  152  160  168  176  184  192  200  208  216  224  232  240
 [31]  248  256  264  272  280  288  296  304  312  320  328  336  344  352  360
 [46]  368  376  384  392  400  408  416  424  432  440  448  456  464  472  480
 [61]  488  496  504  512  520  528  536  544  552  560  568  576  584  592  600
 [76]  608  616  624  632  640  648  656  664  672  680  688  696  704  712  720
 [91]  728  736  744  752  760  768  776  784  792  800  808  816  824  832  840
[106]  848  856  864  872  880  888  896  904  912  920  928  936  944  952  960
[121]  968  976  984  992 1000

or more compactly:

input[(input %% 8) == 0]

Trying to get a multiple of 3 and 5 in R

Try :

p2<-function(x){
    if (x%%3==0){
        return ("Multipleof3")
    } else if (x%%5 == 0){
        return("Multipleof5")
    } else {
        return(x)
    }
}

p<-Vectorize(p2)

p(1:100)

# [1] "1"           "2"           "Multipleof3" "4"           "Multipleof5" "Multipleof3" "7"           "8"   

Note : you can replace p2 by :

p2<-function(x){
    return(ifelse(x%%3==0, "Multipleof3", ifelse(x%%5==0, "Multipleof5", x)))
}

Your function parameter should not be in the question but defined like this : function(x) and when you call the function you put your parameter (1:100) at the place of x. The Vectorize allow to create a new function : p which is the same as p2 but which is capable of handling vectors.

Use :

p2<-function(x){
    return(ifelse(x%%3==0 & x%%5==0, "MultipleOfBoth", ifelse(x%%3==0, "Multipleof3", ifelse(x%%5==0, "Multipleof5", x))))
}

for handling multiple of 3 and 5.

Extracting numbers from vectors of strings

How about

# pattern is by finding a set of numbers in the start and capturing them
as.numeric(gsub("([0-9]+).*$", "\\1", years))

or

# pattern is to just remove _years_old
as.numeric(gsub(" years old", "", years))

or

# split by space, get the element in first index
as.numeric(sapply(strsplit(years, " "), "[[", 1))

Extract elements from a vector that are repeated n times (R)

We can use table if it is based on frequency

v1 <- table(col.vector)
as.integer(names(v1)[v1 == 3])
[1] 3 4

---

If it is based on repeating elements, use rleid

library(data.table)
v1 <- table(rleid(col.vector))
as.integer(names(v1)[v1 == 3])

finding multiples of a number in Python

If you're trying to find the first count multiples of m, something like this would work:

def multiples(m, count):
    for i in range(count):
        print(i*m)

Alternatively, you could do this with range:

def multiples(m, count):
    for i in range(0,count*m,m):
        print(i)

Note that both of these start the multiples at 0 - if you wanted to instead start at m, you'd need to offset it by that much:

range(m,(count+1)*m,m)

Extract multiple ranges from a numeric vector

You were on the right path, and left.open indeed helps, but rightmost.closed actually concerns only the last interval rather than the right "side" of each interval. Hence, we need to use left.open twice. As you yourself figured out, it looks like an optimal way to do that is

x[findInterval(x, v) %% 2 == 1 & findInterval(x, v, left.open = TRUE) %% 2 == 1]
# [1]  2  3  4  9 10 11 18 19

Clearly there are alternatives. E.g.,

fun <- function(x, v)
  if(length(v) > 1) v[1] < x & x < v[2] | fun(x, v[-1:-2]) else FALSE
x[fun(x, v)]
# [1]  2  3  4  9 10 11 18 19

How to extract a specific text from a vector that is separated with multiple commas in R

What about the following?

library(tidyverse)

df %>% 
 mutate(col2 = str_split(col1, "\\s*,\\s*") %>%
   map_chr(~ if (length(.x) %in% 1:2) {.x[length(.x)]} 
      else {.x[length(.x) - 1]}))

#>                              col1   col2
#> 1         book, pencil,eraser,pen eraser
#> 2                        book,pen    pen
#> 3                 music,art,sport    art
#> 4 apple, banana, kiwi, watermelon   kiwi
#> 5            Earth, Mars, Jupiter   Mars

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