R語言paste函數解析
paste函數
paste函數的作用就是將R對象轉換為字符后連接向量。
paste (..., sep = " ", collapse = NULL)
paste0(..., collapse = NULL)
參數
-
... 一個或多個R對象，要轉換為字符向量。
-
sep 分隔字符串。不是NA_character_。
-
collapse 分隔結果的可選字符串。不是NA_character_。
從上參數列表可知，...參數和sep參數是必須參數，collapse參數是可選參數。
其中，
...參數，可以有一個或多個對象。
sep參數，的默認值為空格" " 。
collapse參數因為是可選參數，所以它的默認值就是空NULL。
所以對於paste函數的學習，重點就是學會sep參數和collapse參數。
sep參數顧名思義，就是表示分隔符；
collapse的一個含義是“折疊”，所以表示將一個字符串向量折疊在一起成為一個字符串。
理解sep 和collapse參數
代碼示例用法
> 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默認為空格
> 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設置后，將結果的各個元素連接成一個字符串。
> 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設置后，將一個對象的各個元素連接成一個字符串。
> 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"
與expand.grid函數聯合使用實現循環拼接
代碼示例
> 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
# 首先給出所有元素的搭配組合
> 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
# 每一行的元素組合進行拼接，返回一個字符串向量
> 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"