Better approach to create a sequence-CodePudding

I have an arbitrary data frame, let's say it is of 360 rows which comprises 5 groups, each has 72 rows:

tally <- list(rows = 72, groups = 5)

I want to create a sequence of indexes following this pattern:

1   72 * 0, 1   72 * 1, 1   72 * 2, 1   72 * 3, 1  72 * 4
2   72 * 0, 2   72 * 1, 2   72 * 2, 2   72 * 3, 2  72 * 4
......
71   72 * 0, 1   72 * 1, 1   72 * 2, 1   72 * 3, 1  72 * 4
72   72 * 0, 1   72 * 1, 1   72 * 2, 1   72 * 3, 1  72 * 4

The sequence will be:

1, 73, 145, 217, 289,
2, 74, 146. 218, 290,
......
71, 143, 215, 287, 359,
72, 144, 216, 289, 360

Seems that function seq() doesn't accept vector like this:

seq(from = seq_len(tally$rows), to = tally$rows * tally$rows, by = tally$rows)

So I wrote a function to generate the sequence:

create_indexes_by_group <- function(tally = NULL) {
    bases <- seq_len(tally$rows)
    indexes_list <- lapply(bases, FUN = function(x) {seq(from = x, to = tally$groups * tally$rows, by = tally$rows)})
    
    return(unlist(indexes_list))
}

Is there a shorter way to create the sequence, maybe without introducing dependencies?

CodePudding user response：

We could use rep with seq

out <- with(tally, rep(sequence(rows), each = groups)   
      (rep(rows, each = groups) * (seq(groups) -1)))

-output

 out
  [1]   1  73 145 217 289   2  74 146 218 290   3  75 147 219 291   4  76 148 220 292   5  77 149 221 293   6  78 150 222 294   7  79 151 223 295   8  80 152
 [39] 224 296   9  81 153 225 297  10  82 154 226 298  11  83 155 227 299  12  84 156 228 300  13  85 157 229 301  14  86 158 230 302  15  87 159 231 303  16
 [77]  88 160 232 304  17  89 161 233 305  18  90 162 234 306  19  91 163 235 307  20  92 164 236 308  21  93 165 237 309  22  94 166 238 310  23  95 167 239
[115] 311  24  96 168 240 312  25  97 169 241 313  26  98 170 242 314  27  99 171 243 315  28 100 172 244 316  29 101 173 245 317  30 102 174 246 318  31 103
[153] 175 247 319  32 104 176 248 320  33 105 177 249 321  34 106 178 250 322  35 107 179 251 323  36 108 180 252 324  37 109 181 253 325  38 110 182 254 326
[191]  39 111 183 255 327  40 112 184 256 328  41 113 185 257 329  42 114 186 258 330  43 115 187 259 331  44 116 188 260 332  45 117 189 261 333  46 118 190
[229] 262 334  47 119 191 263 335  48 120 192 264 336  49 121 193 265 337  50 122 194 266 338  51 123 195 267 339  52 124 196 268 340  53 125 197 269 341  54
[267] 126 198 270 342  55 127 199 271 343  56 128 200 272 344  57 129 201 273 345  58 130 202 274 346  59 131 203 275 347  60 132 204 276 348  61 133 205 277
[305] 349  62 134 206 278 350  63 135 207 279 351  64 136 208 280 352  65 137 209 281 353  66 138 210 282 354  67 139 211 283 355  68 140 212 284 356  69 141
[343] 213 285 357  70 142 214 286 358  71 143 215 287 359  72 144 216 288 360