数字四舍五入在公元前猛砸 [英] Rounding Numbers with bc in Bash

问题描述

我要计算与3位数字的平均值，四舍五入取，使用 BC 。

I want to compute an average with 3 decimal figures, rounded to nearest, using bc.

例如：

3,3和5应产生3.667

average of 3, 3 and 5 should yield 3.667

和

3，3和4应该产生3.333

average of 3, 3 and 4 should yield 3.333

我试过：

echo "scale=3; $sum/$n+0.0005" | bc

但扩展如我所料不表现。我能做些什么来解决我的问题？

but scale doesn't behave as I expect. What can I do to solve my problem?

推荐答案

您伎俩添加 0.0005 不是一个坏主意。不过，这并不完全这样的。 比例在内部使用时 BC 执行某些操作（如师）。

Your trick to add 0.0005 is not a bad idea. Though, it doesn't quite work that way. scale is used internally when bc performs some operations (like divisions).

在你的情况，这将是最好先进行分工，也许采用大扩展或 -l <​​/ code>开关置于 BC 1 （如果您的版本支持），然后加入 0.0005 然后设置 =规模3 和执行涉及比例内部有截断执行。操作

In your case, it would be better to perform the division first, maybe using a large scale or the -l switch to bc¹ (if your version supports it), then add 0.0005 and then set scale=3 and perform an operation involving scale internally to have the truncation performed.

是这样的：

`a=$sum/$n+0.0005; scale=3; a/1`

当然，你要进行不同的之是正的还是负的。幸运的是， BC 有一些有条件的经营者。

Of course, you'll want to proceed differently whether sum is positive or negative. Fortunately, bc has some conditional operators.

`a=$sum/$n; if(a>0) a+=0.0005 else if (a<0) a-=0.0005; scale=3; a/1`

您会那么想用格式化这个答案的printf 。

You'll then want to format this answer using printf.

裹函数圆形（在这里你可以随意选择的十进制数字的号码）：

Wrapped in a function round (where you can optionally select the number of decimal figures):

round() {
    # $1 is expression to round (should be a valid bc expression)
    # $2 is number of decimal figures (optional). Defaults to three if none given
    local df=${2:-3}
    printf '%.*f\n' "$df" "$(bc -l <<< "a=$1; if(a>0) a+=5/10^($df+1) else if (a<0) a-=5/10^($df+1); scale=$df; a/1")"
}

试试吧：

gniourf$ round "(3+3+4)/3"
3.333
gniourf$ round "(3+3+5)/3"
3.667
gniourf$ round "-(3+3+5)/3"
-3.667
gniourf$ round 0
0.000
gniourf$ round 1/3 10
0.3333333333
gniourf$ round 0.0005
0.001
gniourf$ round 0.00049
0.000

---

¹ 与 -l <​​/ code>开关，比例设置为 20 ，这应该是足够足够了。

---

¹ with the -l switch, scale is set to 20, which should be plenty enough.

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