这是对哈希进行排序并返回hash对象(而不是Array)的最佳方法吗?

h = {"a"=>1, "c"=>3, "b"=>2, "d"=>4}
# => {"a"=>1, "c"=>3, "b"=>2, "d"=>4}

Hash[h.sort]
# => {"a"=>1, "b"=>2, "c"=>3, "d"=>4}

在Ruby中p和puts有区别吗?

我如何在ruby中写一个循环，以便我可以在每个文件上执行一个代码块?

我是ruby的新手，我已经得出结论，做到这一点的方法是一个do each循环。 ruby文件将在不同于我想要循环的目录的目录中执行。

我已经试过了。foreach，我不能让它工作。

是否有一种简单的方法来运行单个迁移?我不想迁移到某个版本，我只想运行一个特定的版本。

当我试图安装最新版本的compass (https://rubygems.org/gems/compass/versions/1.0.0.alpha.17)时，我得到以下错误。

ERROR:  Error installing compass:
ERROR: Failed to build gem native extension.

 ERROR:  Error installing compass:
  ERROR: Failed to build gem native extension.

    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
checking for ffi.h... no
checking for ffi.h in /usr/local/include,/usr/include/ffi... yes
checking for ffi_call() in -lffi... yes
checking for ffi_prep_closure()... yes
checking for ffi_raw_call()... no
checking for rb_thread_blocking_region()... yes
checking for rb_thread_call_with_gvl()... yes
checking for rb_thread_call_without_gvl()... yes
checking for ffi_prep_cif_var()... no
creating extconf.h
creating Makefile

make "DESTDIR=" clean

make "DESTDIR="
compiling AbstractMemory.c
compiling ArrayType.c
compiling Buffer.c
compiling Call.c
Call.c:303:5: warning: implicit declaration of function 'rb_thread_call_without_gvl' is invalid in C99 [-Wimplicit-function-declaration]
    rbffi_thread_blocking_region(call_blocking_function, data, (void *) -1, NULL);
    ^
./Thread.h:78:39: note: expanded from macro 'rbffi_thread_blocking_region'
# define rbffi_thread_blocking_region rb_thread_call_without_gvl
                                      ^
1 warning generated.
compiling ClosurePool.c
compiling DataConverter.c
DataConverter.c:43:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
compiling DynamicLibrary.c
compiling ffi.c
compiling Function.c
Function.c:479:33: warning: incompatible pointer types passing 'VALUE (void *)' to parameter of type 'void *(*)(void *)' [-Wincompatible-pointer-types]
        rb_thread_call_with_gvl(callback_with_gvl, &cb);
                                ^~~~~~~~~~~~~~~~~
Function.c:102:46: note: passing argument to parameter 'func' here
extern void *rb_thread_call_with_gvl(void *(*func)(void *), void *data1);
                                             ^
Function.c:563:9: warning: implicit declaration of function 'rb_thread_call_without_gvl' is invalid in C99 [-Wimplicit-function-declaration]
        rb_thread_call_without_gvl(async_cb_wait, &w, async_cb_stop, &w);
        ^
Function.c:738:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
3 warnings generated.
compiling FunctionInfo.c
compiling LastError.c
compiling LongDouble.c
compiling MappedType.c
compiling MemoryPointer.c
compiling MethodHandle.c
compiling Platform.c
compiling Pointer.c
compiling Struct.c
compiling StructByReference.c
compiling StructByValue.c
compiling StructLayout.c
compiling Thread.c
compiling Type.c
compiling Types.c
compiling Variadic.c
linking shared-object ffi_c.bundle
clang: error: unknown argument: '-multiply_definedsuppress' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
make: *** [ffi_c.bundle] Error 1

make failed, exit code 2

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/ffi-1.9.3 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-13/2.0.0/ffi-1.9.3/gem_make.out

这是怎么回事?如何正确安装最新的指南针?

正确的方法是什么:

is_array("something") # => false         (or 1)

is_array(["something", "else"]) # => true  (or > 1)

或者获取其中的条目数?

Ruby <=>(太空船)操作符是什么?运算符是否由其他语言实现?

我知道红宝石的“合作”线程使用绿色线程。如何在我的应用程序中创建真正的“操作系统级”线程，以便使用多个cpu内核进行处理?

例如:

9 / 5  #=> 1

但我以为是1.8。我怎样才能得到正确的十进制(非整数)结果?为什么返回1呢?

我通过Ruby宝石“续集”使用PostgreSQL。

我要四舍五入到小数点后两位。

这是我的代码:

SELECT ROUND(AVG(some_column),2)    
FROM table

我得到以下错误:

PG::Error: ERROR:  function round(double precision, integer) does 
not exist (Sequel::DatabaseError)

当我运行以下代码时，我没有得到错误:

SELECT ROUND(AVG(some_column))
FROM table

有人知道我哪里做错了吗?