(This illustrates why screenshots are so iffyâ€”I saw only the two columns.)

There are ways to select columns based on name patterns, but this can be done simply by taking advantage of the regular layout: we want to discard every third column. We can do this by using subsetting based on the column index.

```
dat <- data.frame(
A =c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"), B = 1:26,
C = c("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"),
D = c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"), E = 1:26,
F = c("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"),
G = c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"), H = 1:26,
I = c("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z")
)
dat
#> A B C D E F G H I
#> 1 a 1 A a 1 A a 1 A
#> 2 b 2 B b 2 B b 2 B
#> 3 c 3 C c 3 C c 3 C
#> 4 d 4 D d 4 D d 4 D
#> 5 e 5 E e 5 E e 5 E
#> 6 f 6 F f 6 F f 6 F
#> 7 g 7 G g 7 G g 7 G
#> 8 h 8 H h 8 H h 8 H
#> 9 i 9 I i 9 I i 9 I
#> 10 j 10 J j 10 J j 10 J
#> 11 k 11 K k 11 K k 11 K
#> 12 l 12 L l 12 L l 12 L
#> 13 m 13 M m 13 M m 13 M
#> 14 n 14 N n 14 N n 14 N
#> 15 o 15 O o 15 O o 15 O
#> 16 p 16 P p 16 P p 16 P
#> 17 q 17 Q q 17 Q q 17 Q
#> 18 r 18 R r 18 R r 18 R
#> 19 s 19 S s 19 S s 19 S
#> 20 t 20 T t 20 T t 20 T
#> 21 u 21 U u 21 U u 21 U
#> 22 v 22 V v 22 V v 22 V
#> 23 w 23 W w 23 W w 23 W
#> 24 x 24 X x 24 X x 24 X
#> 25 y 25 Y y 25 Y y 25 Y
#> 26 z 26 Z z 26 Z z 26 Z
# pick out column index numbers that are not divisible by 3 leaving
# no remainder using modulus operator, because that's every third
# column
keepers <- which(1:9 %% 3 != 0)
dat[keepers]
#> A B D E G H
#> 1 a 1 a 1 a 1
#> 2 b 2 b 2 b 2
#> 3 c 3 c 3 c 3
#> 4 d 4 d 4 d 4
#> 5 e 5 e 5 e 5
#> 6 f 6 f 6 f 6
#> 7 g 7 g 7 g 7
#> 8 h 8 h 8 h 8
#> 9 i 9 i 9 i 9
#> 10 j 10 j 10 j 10
#> 11 k 11 k 11 k 11
#> 12 l 12 l 12 l 12
#> 13 m 13 m 13 m 13
#> 14 n 14 n 14 n 14
#> 15 o 15 o 15 o 15
#> 16 p 16 p 16 p 16
#> 17 q 17 q 17 q 17
#> 18 r 18 r 18 r 18
#> 19 s 19 s 19 s 19
#> 20 t 20 t 20 t 20
#> 21 u 21 u 21 u 21
#> 22 v 22 v 22 v 22
#> 23 w 23 w 23 w 23
#> 24 x 24 x 24 x 24
#> 25 y 25 y 25 y 25
#> 26 z 26 z 26 z 26
```