R语言paste函数解析
paste函数
paste函数的作用就是将R对象转换为字符后连接向量。
paste (..., sep = " ", collapse = NULL) paste0(..., collapse = NULL)
参数
... 一个或多个R对象，要转换为字符向量。
sep 分隔字符串。不是NA_character_。
collapse 分隔结果的可选字符串。不是NA_character_。
从上参数列表可知，...参数和sep参数是必须参数，collapse参数是可选参数。
其中，
...参数，可以有一个或多个对象。
sep参数，的默认值为空格" " 。
collapse参数因为是可选参数，所以它的默认值就是空NULL。
所以对于paste函数的学习，重点就是学会sep参数和collapse参数。
理解sep 和collapse参数
代码示例用法
> LETTERS [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" "T" "U" [22] "V" "W" "X" "Y" "Z" > letters [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" [22] "v" "w" "x" "y" "z" # sep默认为空格 > paste(LETTERS,letters) [1] "A a" "B b" "C c" "D d" "E e" "F f" "G g" "H h" "I i" "J j" "K k" "L l" "M m" "N n" [15] "O o" "P p" "Q q" "R r" "S s" "T t" "U u" "V v" "W w" "X x" "Y y" "Z z" > paste(LETTERS,letters, sep = "_") [1] "A_a" "B_b" "C_c" "D_d" "E_e" "F_f" "G_g" "H_h" "I_i" "J_j" "K_k" "L_l" "M_m" "N_n" [15] "O_o" "P_p" "Q_q" "R_r" "S_s" "T_t" "U_u" "V_v" "W_w" "X_x" "Y_y" "Z_z" # collapse设置后，将结果的各个元素连接成一个字符串。 > paste(LETTERS,letters, sep = "_", collapse = '.') [1] "A_a.B_b.C_c.D_d.E_e.F_f.G_g.H_h.I_i.J_j.K_k.L_l.M_m.N_n.O_o.P_p.Q_q.R_r.S_s.T_t.U_u.V_v.W_w.X_x.Y_y.Z_z" # collapse设置后，将一个对象的各个元素连接成一个字符串。 > paste(LETTERS,collapse = '.') [1] "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"
与expand.grid函数联合使用实现循环拼接
代码示例
> LETTERS[1:4] [1] "A" "B" "C" "D" > expand.grid(LETTERS[1:4], 1:4) Var1 Var2 1 A 1 2 B 1 3 C 1 4 D 1 5 A 2 6 B 2 7 C 2 8 D 2 9 A 3 10 B 3 11 C 3 12 D 3 13 A 4 14 B 4 15 C 4 16 D 4 # 首先给出所有元素的搭配组合 > expand.grid(LETTERS[1:4], 1:4) Var1 Var2 1 A 1 2 B 1 3 C 1 4 D 1 5 A 2 6 B 2 7 C 2 8 D 2 9 A 3 10 B 3 11 C 3 12 D 3 13 A 4 14 B 4 15 C 4 16 D 4 # 每一行的元素组合进行拼接，返回一个字符串向量 > apply(expand.grid(LETTERS[1:4], 1:4), 1, paste, collapse = "_") [1] "A_1" "B_1" "C_1" "D_1" "A_2" "B_2" "C_2" "D_2" "A_3" "B_3" "C_3" "D_3" "A_4" "B_4" [15] "C_4" "D_4"
来源：https://www.cnblogs.com/songbiao/p/12529754.html