有时我们想要找到满足特定条件的值的频率。例如，如果我们有一个向量x，它包含从1开始到100结束的随机选择的整数，那么在这种情况下，我们可能想要查找多少个值恰好等于10。这可以通过使用which和length函数来完成。 。
> x1<-rpois(10,5) > x1
输出结果
[1] 5 7 3 3 2 7 3 7 6 3
> length(which(x1==5)) [1] 1 > length(which(x1==7)) [1] 3 > length(which(x1==3)) [1] 4
> x2<-sample(0:9,300,replace=TRUE) > x2
输出结果
[1] 4 1 5 5 5 3 8 9 8 4 8 1 6 3 6 1 0 0 9 4 5 4 5 1 2 3 3 3 4 9 1 4 7 0 7 7 8 [38] 3 5 8 0 3 6 5 0 7 9 8 2 7 3 9 6 5 2 7 6 4 6 3 3 7 7 2 2 6 0 0 1 5 1 2 9 8 [75] 9 9 3 9 0 9 5 7 9 1 0 4 7 2 7 9 9 5 8 9 2 8 1 3 3 8 4 8 5 5 2 4 5 8 0 8 4 [112] 4 5 2 4 5 9 8 5 5 9 4 4 6 6 9 2 5 2 9 0 3 8 7 5 8 1 3 1 0 2 6 8 5 6 1 0 2 [149] 6 3 6 2 4 2 9 2 7 8 3 8 4 7 3 1 9 3 2 0 7 0 3 8 9 7 1 2 3 5 8 9 0 4 6 9 8 [186] 6 7 5 6 3 5 3 4 3 7 6 8 0 1 1 7 8 7 4 1 2 3 9 7 5 0 0 6 3 5 8 1 2 1 6 5 2 [223] 1 0 5 0 8 3 9 2 6 5 2 6 3 7 7 1 4 3 7 6 1 2 3 4 7 2 5 5 5 8 4 2 0 9 1 7 1 [260] 2 1 9 8 2 9 1 5 2 0 5 0 0 1 2 1 7 6 3 8 4 1 9 8 0 9 2 1 6 7 5 1 2 7 2 9 5 [297] 6 8 7 1
> length(which(x2==0)) [1] 26 > length(which(x2==1)) [1] 32 > length(which(x2==2)) [1] 34 > length(which(x2==3)) [1] 31 > length(which(x2==4)) [1] 24 > length(which(x2==5)) [1] 36 > length(which(x2==6)) [1] 25 > length(which(x2==7)) [1] 30 > length(which(x2==8)) [1] 31 > length(which(x2==9)) [1] 31
> x3<-sample(501:999,200) > x3
输出结果
[1] 977 775 630 693 624 602 903 755 819 779 754 914 731 507 946 836 780 826 [19] 718 899 762 897 583 880 712 669 551 620 959 753 832 835 786 725 803 881 [37] 520 541 795 691 957 888 635 738 562 673 746 665 807 855 666 778 664 657 [55] 985 752 701 967 513 548 997 504 814 722 646 893 992 975 675 645 870 760 [73] 920 894 909 770 982 613 817 581 651 704 568 911 763 523 766 872 929 816 [91] 535 518 956 689 802 848 822 621 506 632 991 811 842 570 923 838 873 567 [109] 812 720 884 958 653 879 854 859 663 919 680 833 601 994 988 576 839 950 [127] 698 768 649 517 626 867 690 594 952 623 895 783 892 970 785 815 672 813 [145] 863 682 986 707 948 983 544 622 606 761 937 906 990 740 688 844 799 684 [163] 589 960 998 976 515 627 925 658 685 913 694 596 784 933 687 522 503 600 [181] 751 558 856 525 963 827 514 907 774 579 509 508 700 717 900 656 918 901 [199] 532 829
> length(which(x3==501)) [1] 0 > length(which(x3==502)) [1] 0 > length(which(x3==620)) [1] 1 > length(which(x3==920)) [1] 1
> x4<-round(runif(300,5,10),0) > x4
输出结果
[1] 8 5 9 5 9 10 8 5 6 7 8 10 7 5 8 10 10 9 7 6 9 6 10 8 9 [26] 10 7 6 7 10 9 9 8 5 9 6 5 7 7 8 5 7 7 7 6 7 9 9 9 9 [51] 6 8 9 8 8 6 5 8 9 9 5 9 9 6 8 9 6 6 7 10 9 7 9 8 9 [76] 10 8 9 6 10 7 8 10 6 6 6 7 5 7 5 10 10 7 5 10 6 7 7 6 5 [101] 5 7 7 10 10 10 9 10 9 8 10 9 9 7 10 8 10 9 6 9 8 9 8 7 6 [126] 9 10 7 8 9 5 6 6 10 5 5 8 9 7 8 5 6 9 8 10 6 10 6 7 5 [151] 6 6 8 5 8 9 10 7 6 8 7 8 5 7 7 8 8 9 7 6 5 9 8 6 9 [176] 6 7 8 5 5 5 10 8 5 9 7 5 7 9 9 6 9 8 9 6 10 7 5 9 6 [201] 9 7 6 5 9 6 5 8 7 8 6 7 7 8 8 9 9 7 9 6 8 7 9 8 8 [226] 9 6 7 9 9 5 7 6 8 9 10 9 9 8 9 7 5 7 5 8 5 9 5 6 7 [251] 6 7 7 5 7 10 7 8 8 7 7 9 10 6 6 9 9 7 8 10 6 8 6 7 7 [276] 10 9 8 10 7 9 9 9 8 7 6 9 7 9 8 5 6 10 6 10 8 9 7 8 10
> length(which(x4==5)) [1] 37 > length(which(x4==6)) [1] 48 > length(which(x4==7)) [1] 59 > length(which(x4==8)) [1] 52 > length(which(x4==9)) [1] 67 > length(which(x4==10)) [1] 37
> x5<-sample(11:15,150,replace=TRUE) > x5
输出结果
[1] 12 15 12 11 15 15 15 15 13 12 12 11 15 15 13 15 15 14 14 12 15 11 13 14 11 [26] 13 13 15 13 13 15 12 13 15 12 12 12 13 14 13 12 14 15 11 14 13 14 14 12 13 [51] 11 11 13 11 12 12 15 15 14 11 11 11 14 13 14 13 12 12 11 12 12 14 13 13 15 [76] 11 11 14 14 14 14 12 11 12 13 15 12 12 15 14 14 13 12 13 15 11 11 14 13 12 [101] 15 14 15 12 13 13 15 11 14 11 14 15 12 11 13 13 12 11 15 12 13 14 11 15 12 [126] 12 11 14 15 12 12 14 14 11 14 11 12 13 12 15 13 11 15 11 13 12 12 14 13 11
> length(which(x5==11)) [1] 28 > length(which(x5==12)) [1] 35 > length(which(x5==13)) [1] 30 > length(which(x5==14)) [1] 28 > length(which(x5==15)) [1] 29