在常见的 lisp 中，如何格式化浮点数并指定分组、群聊和小数点分隔符 char
In common lisp how can I format a floating point and specify grouping, group char and decimal separator char
假设我有浮点数 1234.9
我想将其格式化为1.234,90
是否有格式指令组合？ ~D 可以处理分组和组字符，只处理整数。 ~F 根本不处理分组。据我所知 none 可以将小数点从 . 更改为 ,
我看到的唯一解决方案是将 ~D 用于整数部分数字分组并将其与 , 和小数部分连接起来。有更好的想法吗？
正如 jkiiski 的评论所建议的，您可以使用 ~/func/ 指令。
这只是一个示例，您可以使用函数进行更详细的说明：
CL-USER> (defun q(stream arg &rest args)
(declare (ignore args))
(format stream
"~,,'.,:D,~a"
(truncate arg)
(let ((float-string (format nil "~f" arg)))
(subseq float-string (1+ (position #\. float-string))))))
Q
CL-USER> (format t "~/q/~%" 1024.36)
1.024,36
NIL
CL-USER> (format t "~/q/~%" -1024.36)
-1.024,36
NIL
已编辑
第一个版本有 round，这是错误的，truncate 是正确的运算符。
如果您不介意拆分整数和小数部分，您可以执行以下操作：
(multiple-value-bind (int rest) (floor 1234.56)
(let ((rest (round (* rest 1000))))
(format t "~,,'.,:D,~D~%" int rest)))
1.234,560
四舍五入前的乘法表示您要打印逗号后的位数。不确定这种方法是否能很好地实现精确打印的自动控制，即 1.5 打印为“1,5”而不是“1,500”。
其他答案目前使用 round，这可能不是向上舍入（正数）或向下舍入（负数）时的预期行为。这是 ~/custom/ 指令的另一种方法，主要来自 Renzo 的回答。
(defun custom (stream number &rest args)
(declare (ignore args))
(multiple-value-bind (integer decimal) (truncate number)
(format stream "~,,'.,:D~@[,~a~]"
integer
(unless (zerop decimal)
(let ((decimal-string (princ-to-string (abs decimal))))
(subseq decimal-string (1+ (position #\. decimal-string))))))))
测试
(loop for i in '(1034.34 -223.12 -10.0 10.0 14 324 1020231)
collect (custom nil i))
=> ("1.034,33996582" "-223,11999512" "-10" "10" "14" "324" "1.020.231")
您可以定义一个用 tilde-slash 调用的函数，大多数其他答案已经完成了，但是为了获得类似于 ~F 的输出，但注入了逗号字符，并使用了小数点替换，我觉得最好调用get ~F产生的输出，然后修改写入字符串。这是一种方法，使用实用程序 inject-comma 以指定的间隔向字符串添加逗号字符。这是指令函数：
(defun print-float (stream arg colonp atp
&optional
(point-char #\.)
(comma-char #\,)
(comma-interval 3))
"A function for printing floating point numbers, with an interface
suitable for use with the tilde-slash FORMAT directive. The full form
is
~point-char,comma-char,comma-interval/print-float/
The point-char is used in place of the decimal point, and defaults to
#\. If : is specified, then the whole part of the number will be
grouped in the same manner as ~D, using COMMA-CHAR and COMMA-INTERVAL.
If @ is specified, then the sign is always printed."
(let* ((sign (if (minusp arg) "-" (if (and atp (plusp arg)) "+" "")))
(output (format nil "~F" arg))
(point (position #\. output :test 'char=))
(whole (subseq output (if (minusp arg) 1 0) point))
(fractional (subseq output (1+ point))))
(when colonp
(setf whole (inject-comma whole comma-char comma-interval)))
(format stream "~A~A~C~A"
sign whole point-char fractional)))
这里有一些例子：
(progn
;; with @ (for sign) and : (for grouping)
(format t "~','.2@:/print-float/ ~%" 12345.6789) ;=> +1.23.45,679
;; with no @ (no sign) and : (for grouping)
(format t "~'.'_3:/print-float/ ~%" 12345.678) ;=> 12_345.678
;; no @ (but sign, since negative) and : (for grouping)
(format t "~'.'_3:/print-float/ ~%" -12345.678) ;=> -12_345.678
;; no @ (no sign) and no : (no grouping)
(format t "~'.'_3@/print-float/ ~%" 12345.678)) ;=> +12345.678 (no :)
以下是来自 的例子，它实际上帮助我发现了负数的错误：
CL-USER> (loop for i in '(1034.34 -223.12 -10.0 10.0 14 324 1020231)
do (format t "~','.:/print-float/~%" i))
1.034,34
-223,12
-10,0
10,0
14,0
324,0
1.020.231,0
NIL
这里是inject-comma，还有一些例子：
(defun inject-comma (string comma-char comma-interval)
(let* ((len (length string))
(offset (mod len comma-interval)))
(with-output-to-string (out)
(write-string string out :start 0 :end offset)
(do ((i offset (+ i comma-interval)))
((>= i len))
(unless (zerop i)
(write-char comma-char out))
(write-string string out :start i :end (+ i comma-interval))))))
(inject-comma "1234567" #\, 3)
;;=> "1,234,567"
(inject-comma "1234567" #\. 2)
;;=> "1.23.45.67"
我已经找到了这个正数的小解决方案。
(defun comma-point (stream arg &rest args)
(declare (ignore args))
(multiple-value-bind (i r) (truncate arg)
(format stream "~,,',,:D.~2,'0D" i (truncate (* 100 r)))))
;; ^ ^
;; | `Decimal point
;; `Thousands separator
(defun point-comma (stream arg &rest args)
(declare (ignore args))
(multiple-value-bind (i r) (truncate arg)
(format stream "~,,'.,:D,~2,'0D" i (truncate (* 100 r)))))
(defun space-comma (stream arg &rest args)
(declare (ignore args))
(multiple-value-bind (i r) (truncate arg)
(format stream "~,,' ,:D,~2,'0D" i (truncate (* 100 r)))))
检测人数：
(dolist (value '(1034.34 -223.12 -10.0 10.0 14 324 1020231.099))
(format t "~16@A" (format nil "~/comma-point/" value))
(format t "~16@A" (format nil "~/point-comma/" value))
(format t "~16@A~%" (format nil "~/space-comma/" value)))
;; 1,034.33 1.034,33 1 034,33
;; -223.-11 -223,-11 -223,-11
;; -10.00 -10,00 -10,00
;; 10.00 10,00 10,00
;; 14.00 14,00 14,00
;; 324.00 324,00 324,00
;; 1,020,231.12 1.020.231,12 1 020 231,12
第二个测试数字表明它不适用于负数 (-223.11 => -223,-11)。此外，使用 truncate（或 other similar functions）意味着会出现准确性损失，如上次测试编号所示（1020231.099 => 1.020.231,12）。
假设我有浮点数 1234.9
我想将其格式化为1.234,90
是否有格式指令组合？ ~D 可以处理分组和组字符，只处理整数。 ~F 根本不处理分组。据我所知 none 可以将小数点从 . 更改为 ,
我看到的唯一解决方案是将 ~D 用于整数部分数字分组并将其与 , 和小数部分连接起来。有更好的想法吗？
正如 jkiiski 的评论所建议的，您可以使用 ~/func/ 指令。
这只是一个示例，您可以使用函数进行更详细的说明：
CL-USER> (defun q(stream arg &rest args)
(declare (ignore args))
(format stream
"~,,'.,:D,~a"
(truncate arg)
(let ((float-string (format nil "~f" arg)))
(subseq float-string (1+ (position #\. float-string))))))
Q
CL-USER> (format t "~/q/~%" 1024.36)
1.024,36
NIL
CL-USER> (format t "~/q/~%" -1024.36)
-1.024,36
NIL
已编辑
第一个版本有 round，这是错误的，truncate 是正确的运算符。
如果您不介意拆分整数和小数部分，您可以执行以下操作：
(multiple-value-bind (int rest) (floor 1234.56)
(let ((rest (round (* rest 1000))))
(format t "~,,'.,:D,~D~%" int rest)))
1.234,560
四舍五入前的乘法表示您要打印逗号后的位数。不确定这种方法是否能很好地实现精确打印的自动控制，即 1.5 打印为“1,5”而不是“1,500”。
其他答案目前使用 round，这可能不是向上舍入（正数）或向下舍入（负数）时的预期行为。这是 ~/custom/ 指令的另一种方法，主要来自 Renzo 的回答。
(defun custom (stream number &rest args)
(declare (ignore args))
(multiple-value-bind (integer decimal) (truncate number)
(format stream "~,,'.,:D~@[,~a~]"
integer
(unless (zerop decimal)
(let ((decimal-string (princ-to-string (abs decimal))))
(subseq decimal-string (1+ (position #\. decimal-string))))))))
测试
(loop for i in '(1034.34 -223.12 -10.0 10.0 14 324 1020231)
collect (custom nil i))
=> ("1.034,33996582" "-223,11999512" "-10" "10" "14" "324" "1.020.231")
您可以定义一个用 tilde-slash 调用的函数，大多数其他答案已经完成了，但是为了获得类似于 ~F 的输出，但注入了逗号字符，并使用了小数点替换，我觉得最好调用get ~F产生的输出，然后修改写入字符串。这是一种方法，使用实用程序 inject-comma 以指定的间隔向字符串添加逗号字符。这是指令函数：
(defun print-float (stream arg colonp atp
&optional
(point-char #\.)
(comma-char #\,)
(comma-interval 3))
"A function for printing floating point numbers, with an interface
suitable for use with the tilde-slash FORMAT directive. The full form
is
~point-char,comma-char,comma-interval/print-float/
The point-char is used in place of the decimal point, and defaults to
#\. If : is specified, then the whole part of the number will be
grouped in the same manner as ~D, using COMMA-CHAR and COMMA-INTERVAL.
If @ is specified, then the sign is always printed."
(let* ((sign (if (minusp arg) "-" (if (and atp (plusp arg)) "+" "")))
(output (format nil "~F" arg))
(point (position #\. output :test 'char=))
(whole (subseq output (if (minusp arg) 1 0) point))
(fractional (subseq output (1+ point))))
(when colonp
(setf whole (inject-comma whole comma-char comma-interval)))
(format stream "~A~A~C~A"
sign whole point-char fractional)))
这里有一些例子：
(progn
;; with @ (for sign) and : (for grouping)
(format t "~','.2@:/print-float/ ~%" 12345.6789) ;=> +1.23.45,679
;; with no @ (no sign) and : (for grouping)
(format t "~'.'_3:/print-float/ ~%" 12345.678) ;=> 12_345.678
;; no @ (but sign, since negative) and : (for grouping)
(format t "~'.'_3:/print-float/ ~%" -12345.678) ;=> -12_345.678
;; no @ (no sign) and no : (no grouping)
(format t "~'.'_3@/print-float/ ~%" 12345.678)) ;=> +12345.678 (no :)
以下是来自
CL-USER> (loop for i in '(1034.34 -223.12 -10.0 10.0 14 324 1020231)
do (format t "~','.:/print-float/~%" i))
1.034,34
-223,12
-10,0
10,0
14,0
324,0
1.020.231,0
NIL
这里是inject-comma，还有一些例子：
(defun inject-comma (string comma-char comma-interval)
(let* ((len (length string))
(offset (mod len comma-interval)))
(with-output-to-string (out)
(write-string string out :start 0 :end offset)
(do ((i offset (+ i comma-interval)))
((>= i len))
(unless (zerop i)
(write-char comma-char out))
(write-string string out :start i :end (+ i comma-interval))))))
(inject-comma "1234567" #\, 3)
;;=> "1,234,567"
(inject-comma "1234567" #\. 2)
;;=> "1.23.45.67"
我已经找到了这个正数的小解决方案。
(defun comma-point (stream arg &rest args)
(declare (ignore args))
(multiple-value-bind (i r) (truncate arg)
(format stream "~,,',,:D.~2,'0D" i (truncate (* 100 r)))))
;; ^ ^
;; | `Decimal point
;; `Thousands separator
(defun point-comma (stream arg &rest args)
(declare (ignore args))
(multiple-value-bind (i r) (truncate arg)
(format stream "~,,'.,:D,~2,'0D" i (truncate (* 100 r)))))
(defun space-comma (stream arg &rest args)
(declare (ignore args))
(multiple-value-bind (i r) (truncate arg)
(format stream "~,,' ,:D,~2,'0D" i (truncate (* 100 r)))))
检测人数：
(dolist (value '(1034.34 -223.12 -10.0 10.0 14 324 1020231.099))
(format t "~16@A" (format nil "~/comma-point/" value))
(format t "~16@A" (format nil "~/point-comma/" value))
(format t "~16@A~%" (format nil "~/space-comma/" value)))
;; 1,034.33 1.034,33 1 034,33
;; -223.-11 -223,-11 -223,-11
;; -10.00 -10,00 -10,00
;; 10.00 10,00 10,00
;; 14.00 14,00 14,00
;; 324.00 324,00 324,00
;; 1,020,231.12 1.020.231,12 1 020 231,12
第二个测试数字表明它不适用于负数 (-223.11 => -223,-11)。此外，使用 truncate（或 other similar functions）意味着会出现准确性损失，如上次测试编号所示（1020231.099 => 1.020.231,12）。