How to extract multiple numbers from a vector from R

Question

I have a vector let's say

x <- 1:1000

and I want to extract multiples of 8 from it.

What should I do? (I do not want to do x[-c(8,16,24,.....)] )

The goal is to remove the multiples of 8 from x vector

Answer 1

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 there are 2 left, i.e. 320 is exactly 40 times 8, leaving 2.

In your example, we can use %% in combination with a subset to get a multiplicity of 8. Remember that %% gives 0 for exact multiple values ​​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 vector operation, i.e. the left side is a vector, the result will also be a vector. Now the multiple_of_8 vector contains 1000 logical systems indicating whether this particular input element is an exact multiple of 8. Using this logical vector for a subset, you will get 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 compact:

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