如何在bash中生成相等数量的两个值

Question

我需要在 bash 中随机生成一系列“a”和“-a”。我必须有相同数量的“a”和“-a”，这意味着数组的总和应该为零。类似的东西：

n=20;
for i in seq 1 1 n
do
    if test $RANDOM -ge 16378
    then
        a=1
    else
        a=-1
    fi
done

与此类似的东西会随机生成“a”和“-a”，但总和并不总是为零。我应该如何在代码中应用这个条件？！

感谢

Answer 1

我添加了一个单独的答案，因为您实际上可能正在寻找更简单的东西。如果你想循环遍历 20 个值，其中 10 个是 1，其中 10 个是 -1，按随机顺序，我会这样做：

$ for i in {1..10}; do echo 1; echo -1; done | shuf
-1
1
-1
1
-1
1
-1
1
1
1
-1
1
-1
-1
-1
-1
1
1
1
-1

Answer 2

我将您的问题解释为等同于创建一个已知长度的数组，其中包含一定数量的a 和相同数量的-a，然后得到该数组的随机排列。

您需要在bash 中进行吗？如果是这样，您可以先创建所需长度的数组，然后对其进行随机播放。

来自BashFaq：

此函数使用 Knuth-Fisher-Yates 洗牌算法就地洗牌数组的元素。

#!/bin/bash

shuffle() {
   local i tmp size max rand

   # $RANDOM % (i+1) is biased because of the limited range of $RANDOM
   # Compensate by using a range which is a multiple of the array size.
   size=${#array[*]}
   max=$(( 32768 / size * size ))

   for ((i=size-1; i>0; i--)); do
      while (( (rand=$RANDOM) >= max )); do :; done
      rand=$(( rand % (i+1) ))
      tmp=${array[i]} array[i]=${array[rand]} array[rand]=$tmp
   done
}

（复制自Simple method to shuffle the elements of an array in BASH shell?）

如果您不限于bash，您可以只使用shuf 和for 循环到do it as a one-liner。

Answer 3

很简单，你只需要学会更好地使用 RANDOM。

要获得一个范围内的随机数，然后按范围的长度对其进行修改。在这种情况下，它是二进制的，所以 $((RANDOM % 2))

declare -i total=0     # you need to define this as an integer for += later
for i in {1..20}; do
   declare -i num=$((RANDOM % 2))  # define an integer var
   [ $num -lt 1 ] && ((--num))     # if it's zero, change to -1
   echo $num      # see the number picked
   total+=$num
done
echo "total = $total"

我假设您想查看结果。如果你想对它求和，那么我们会在循环外声明一个变量，然后使用它。我会编辑它。

Answer 4

这可能是你想要的。它产生一个随机数的 'a's 和 '-a's 组合，每个数字的一​​半，使字符串中的 'a's 的数量等于字符串中的 '-a's 的数量。如果我误解了这个问题，请告诉我。 可以限制字符串的最大长度，如果需要请告诉我

# l represents half the length of the array
l=1; # Sets l to 1, set the following while statement evaluates true
# Sets l to $RANDOM until it is an even number 
while [ $((l % 2)) -ne 0 ]; do 
    l=$RANDOM; 
done;
echo $l;
# Sets m and n to l
n=$l; # n is the number of 'a's 
m=$l; # m is the number of '-a's
# Initialises result as an empty string
result="";
# Doesn't stop until both 'a's and '-a's have been exhausted, i.e. n and m both equal 0
while [ "$n" != "0" ] && [ "$m" != "0" ]; do
    # Decides between 'a' and '-a'
    i=$(($RANDOM % 2));
    # Evaluates true if $i is 0, and the number of '-a's has not been exhausted, however also evaluates true if the number of '-a's has been exhausted
    if ([ "$i" == "0" ] && [ "$n" != "0" ]) || [ "$m" == "0" ]; then
        # Appends 'a' to result
        result="$result a";
        # Decrement the amount of 'a's left
        n=$((n-1));
    # Evaluates true if $i is 1, and the number of 'a's has not been exhausted, however also evaluates true if the number of 'a's has been exhausted
    elif ([ "$i" == "1" ] && [ "$m" != "0" ]) || [ "$n" == "0" ]; then
        # Appends '-a' to result
        result="$result -a";
        # Decrements the amount of '-a's left
        m=$((m-1));
    fi; 
done;
# Prints the result
echo $result;

编辑：根据 SaintHax 的建议，已添加代码注释