为什么 awk 似乎随机化数组? [英] Why does awk seem to randomize the array?

问题描述

如果您查看此 awk 测试的输出，您会看到 awk 中的 array 似乎以某种随机模式打印.对于相同数量的输入，它似乎是相同的顺序.为什么会这样?

If you look at output of this awk test, you see that array in awk seems to be printed at some random pattern. It seems to be in same order for same number of input. Why does it do so?

echo "one two three four five six" | awk '{for (i=1;i<=NF;i++) a[i]=$i} END {for (j in a) print j,a[j]}'
4 four
5 five
6 six
1 one
2 two
3 three

echo "P04637 1A1U 1AIE 1C26 1DT7 1GZH 1H26 1HS5 1JSP 1KZY 1MA3 1OLG 1OLH 1PES 1PET 1SAE 1SAF 1SAK 1SAL 1TSR 1TUP 1UOL 1XQH 1YC5 1YCQ" | awk '{for (i=1;i<=NF;i++) a[i]=$i} END {for (j in a) print j,a[j]}'
17 1SAF
4 1C26
18 1SAK
5 1DT7
19 1SAL
6 1GZH
7 1H26
8 1HS5
9 1JSP
10 1KZY
20 1TSR
11 1MA3
21 1TUP
12 1OLG
22 1UOL
13 1OLH
23 1XQH
14 1PES
1 P04637
24 1YC5
15 1PET
2 1A1U
25 1YCQ
16 1SAE
3 1AIE

为什么会这样，有什么规定吗?

Why does it do so, is there rule for this?

推荐答案

来自 8.awk 中的数组 --> GNU Awk 用户指南中的 8.5 Scanning All Elements of an Array 参考 for (value in array) 语法:

From 8. Arrays in awk --> 8.5 Scanning All Elements of an Array in the GNU Awk user's guide when referring to the for (value in array) syntax:

this 访问数组元素的顺序语句由数组的内部排列决定awk 中的元素，无法控制或更改.这可以导致如果通过语句中的语句将新元素添加到数组中的问题循环体；无法预测 for 循环是否会到达他们.同样，在循环内改变 var 可能会产生奇怪的结果.最好避免这样的事情.

The order in which elements of the array are accessed by this statement is determined by the internal arrangement of the array elements within awk and cannot be controlled or changed. This can lead to problems if new elements are added to array by statements in the loop body; it is not predictable whether or not the for loop will reach them. Similarly, changing var inside the loop may produce strange results. It is best to avoid such things.

<小时>

所以如果你想按照你存储的顺序打印数组，那么你必须使用经典的for循环:

for (j=1; j<=NF; j++) print j,a[j]

示例:

$ awk '{for (i=1;i<=NF;i++) a[i]=$i} END {for (j=1; j<=NF; j++) print j,a[j]}' <<< "P04637 1A1U 1AIE 1C26 1DT7 1GZH 1H26 1HS5 1JSP 1KZY 1MA3 1OLG 1OLH 1PES 1PET 1SAE 1SAF 1SAK 1SAL 1TSR 1TUP 1UOL 1XQH 1YC5 1YCQ"
1 P04637
2 1A1U
3 1AIE
4 1C26
5 1DT7
6 1GZH
7 1H26
8 1HS5
9 1JSP
10 1KZY
11 1MA3
12 1OLG
13 1OLH
14 1PES
15 1PET
16 1SAE
17 1SAF
18 1SAK
19 1SAL
20 1TSR
21 1TUP
22 1UOL
23 1XQH
24 1YC5
25 1YCQ

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