Try it this way
testset <- seq(1:16384)
testset <- matrix(testset, nrow = 256, byrow = TRUE)
head(testset)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13]
#> [1,] 1 2 3 4 5 6 7 8 9 10 11 12 13
#> [2,] 65 66 67 68 69 70 71 72 73 74 75 76 77
#> [3,] 129 130 131 132 133 134 135 136 137 138 139 140 141
#> [4,] 193 194 195 196 197 198 199 200 201 202 203 204 205
#> [5,] 257 258 259 260 261 262 263 264 265 266 267 268 269
#> [6,] 321 322 323 324 325 326 327 328 329 330 331 332 333
#> [,14] [,15] [,16] [,17] [,18] [,19] [,20] [,21] [,22] [,23] [,24]
#> [1,] 14 15 16 17 18 19 20 21 22 23 24
#> [2,] 78 79 80 81 82 83 84 85 86 87 88
#> [3,] 142 143 144 145 146 147 148 149 150 151 152
#> [4,] 206 207 208 209 210 211 212 213 214 215 216
#> [5,] 270 271 272 273 274 275 276 277 278 279 280
#> [6,] 334 335 336 337 338 339 340 341 342 343 344
#> [,25] [,26] [,27] [,28] [,29] [,30] [,31] [,32] [,33] [,34] [,35]
#> [1,] 25 26 27 28 29 30 31 32 33 34 35
#> [2,] 89 90 91 92 93 94 95 96 97 98 99
#> [3,] 153 154 155 156 157 158 159 160 161 162 163
#> [4,] 217 218 219 220 221 222 223 224 225 226 227
#> [5,] 281 282 283 284 285 286 287 288 289 290 291
#> [6,] 345 346 347 348 349 350 351 352 353 354 355
#> [,36] [,37] [,38] [,39] [,40] [,41] [,42] [,43] [,44] [,45] [,46]
#> [1,] 36 37 38 39 40 41 42 43 44 45 46
#> [2,] 100 101 102 103 104 105 106 107 108 109 110
#> [3,] 164 165 166 167 168 169 170 171 172 173 174
#> [4,] 228 229 230 231 232 233 234 235 236 237 238
#> [5,] 292 293 294 295 296 297 298 299 300 301 302
#> [6,] 356 357 358 359 360 361 362 363 364 365 366
#> [,47] [,48] [,49] [,50] [,51] [,52] [,53] [,54] [,55] [,56] [,57]
#> [1,] 47 48 49 50 51 52 53 54 55 56 57
#> [2,] 111 112 113 114 115 116 117 118 119 120 121
#> [3,] 175 176 177 178 179 180 181 182 183 184 185
#> [4,] 239 240 241 242 243 244 245 246 247 248 249
#> [5,] 303 304 305 306 307 308 309 310 311 312 313
#> [6,] 367 368 369 370 371 372 373 374 375 376 377
#> [,58] [,59] [,60] [,61] [,62] [,63] [,64]
#> [1,] 58 59 60 61 62 63 64
#> [2,] 122 123 124 125 126 127 128
#> [3,] 186 187 188 189 190 191 192
#> [4,] 250 251 252 253 254 255 256
#> [5,] 314 315 316 317 318 319 320
#> [6,] 378 379 380 381 382 383 384
Created on 2019-01-17 by the reprex package (v0.2.1)
flodel: https://stackoverflow.com/questions/17752830/r-reshape-a-vector-into-multiple-columns