I have a matrix of order 2192*23, I want to choose the rows number "3rd", "4th", "10th", "11th", "17th", "18th", "24th", "25th" and so on
[3,4,10,11,17,18,24,25,31,32,38,39,45,46,...]
continue till the last row in the above order. how I will do this in R?
a1 <- c(3, 4)
d <- 7
n <- 10
S1 <- a1[1] + d * (seq(n) - 1)
S2 <- a1[2] + d * (seq(n) - 1)
sort(c(S1, S2))
#> [1] 3 4 10 11 17 18 24 25 31 32 38 39 45 46 52 53 59 60 66 67
library(magrittr)
sapply(a1, function(x) (x + d * (seq(n) - 1))) %>%
matrix(ncol = 1) %>%
sort
#> [1] 3 4 10 11 17 18 24 25 31 32 38 39 45 46 52 53 59 60 66 67
Created on 2022-01-18 by the reprex package (v2.0.1)
We can use outer + seq
> c(outer(0:1, seq(3, 2192, by = 7), `+`))
[1] 3 4 10 11 17 18 24 25 31 32 38 39 45 46 52
[16] 53 59 60 66 67 73 74 80 81 87 88 94 95 101 102
[31] 108 109 115 116 122 123 129 130 136 137 143 144 150 151 157
[46] 158 164 165 171 172 178 179 185 186 192 193 199 200 206 207
[61] 213 214 220 221 227 228 234 235 241 242 248 249 255 256 262
[76] 263 269 270 276 277 283 284 290 291 297 298 304 305 311 312
[91] 318 319 325 326 332 333 339 340 346 347 353 354 360 361 367
[106] 368 374 375 381 382 388 389 395 396 402 403 409 410 416 417
[121] 423 424 430 431 437 438 444 445 451 452 458 459 465 466 472
[136] 473 479 480 486 487 493 494 500 501 507 508 514 515 521 522
[151] 528 529 535 536 542 543 549 550 556 557 563 564 570 571 577
[166] 578 584 585 591 592 598 599 605 606 612 613 619 620 626 627
[181] 633 634 640 641 647 648 654 655 661 662 668 669 675 676 682
[196] 683 689 690 696 697 703 704 710 711 717 718 724 725 731 732
[211] 738 739 745 746 752 753 759 760 766 767 773 774 780 781 787
[226] 788 794 795 801 802 808 809 815 816 822 823 829 830 836 837
[241] 843 844 850 851 857 858 864 865 871 872 878 879 885 886 892
[256] 893 899 900 906 907 913 914 920 921 927 928 934 935 941 942
[271] 948 949 955 956 962 963 969 970 976 977 983 984 990 991 997
[286] 998 1004 1005 1011 1012 1018 1019 1025 1026 1032 1033 1039 1040 1046 1047
[301] 1053 1054 1060 1061 1067 1068 1074 1075 1081 1082 1088 1089 1095 1096 1102
[316] 1103 1109 1110 1116 1117 1123 1124 1130 1131 1137 1138 1144 1145 1151 1152
[331] 1158 1159 1165 1166 1172 1173 1179 1180 1186 1187 1193 1194 1200 1201 1207
[346] 1208 1214 1215 1221 1222 1228 1229 1235 1236 1242 1243 1249 1250 1256 1257
[361] 1263 1264 1270 1271 1277 1278 1284 1285 1291 1292 1298 1299 1305 1306 1312
[376] 1313 1319 1320 1326 1327 1333 1334 1340 1341 1347 1348 1354 1355 1361 1362
[391] 1368 1369 1375 1376 1382 1383 1389 1390 1396 1397 1403 1404 1410 1411 1417
[406] 1418 1424 1425 1431 1432 1438 1439 1445 1446 1452 1453 1459 1460 1466 1467
[421] 1473 1474 1480 1481 1487 1488 1494 1495 1501 1502 1508 1509 1515 1516 1522
[436] 1523 1529 1530 1536 1537 1543 1544 1550 1551 1557 1558 1564 1565 1571 1572
[451] 1578 1579 1585 1586 1592 1593 1599 1600 1606 1607 1613 1614 1620 1621 1627
[466] 1628 1634 1635 1641 1642 1648 1649 1655 1656 1662 1663 1669 1670 1676 1677
[481] 1683 1684 1690 1691 1697 1698 1704 1705 1711 1712 1718 1719 1725 1726 1732
[496] 1733 1739 1740 1746 1747 1753 1754 1760 1761 1767 1768 1774 1775 1781 1782
[511] 1788 1789 1795 1796 1802 1803 1809 1810 1816 1817 1823 1824 1830 1831 1837
[526] 1838 1844 1845 1851 1852 1858 1859 1865 1866 1872 1873 1879 1880 1886 1887
[541] 1893 1894 1900 1901 1907 1908 1914 1915 1921 1922 1928 1929 1935 1936 1942
[556] 1943 1949 1950 1956 1957 1963 1964 1970 1971 1977 1978 1984 1985 1991 1992
[571] 1998 1999 2005 2006 2012 2013 2019 2020 2026 2027 2033 2034 2040 2041 2047
[586] 2048 2054 2055 2061 2062 2068 2069 2075 2076 2082 2083 2089 2090 2096 2097
[601] 2103 2104 2110 2111 2117 2118 2124 2125 2131 2132 2138 2139 2145 2146 2152
[616] 2153 2159 2160 2166 2167 2173 2174 2180 2181 2187 2188
Using vector recycling -
ind <- seq_len(nrow(mat))
#ind <- seq_len(2192)
ind[c(F, F, T, T, F, F, F)]
#[1] 3 4 10 11 17 18 24 25 31 32 38 39 45 46 52
#[16] 53 59 60 66 67 73 74 80 81 87 88 94 95 101 102
#...
#...
Another way is to use sequence
n = 2192/7
s <- sequence(nvec = rep(2, n), from = (7*1:n)-4)
# [1] 3 4 10 11 17 18 24 25 31 32 38 39 45 46 52 53 59 60 66 67 73 74
# ...