4.4: Variable Number of arguments

Last updated
Save as PDF

Page ID: 63967

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

From the last exercise, it would be unfortunate if we have to write different functions for different number of arguments. We can write a variable number of arguments with a ... trailing the last argument. The following is a generalized version of the mean:

function theMean(x::Number...) 
  local sum=0
  for val in x
    sum += val 
  end
  sum/length(x)
end

which uses a for loop that we will discuss later. This function will now find the mean using any number of arguments.

theMean(1,2,3,4)

Also, note that the argument x with the ... is a tuple, (see section 3.9). An alternative way to access the individual elements of x would be to use brackets. For example, x[3] would be the third argument.

Exercise

Try the following (replace the code in the above code block) and notice the resulting type:

theMean(11//2,5//6,1//9)
theMean(1.0,2.0,3.0,4.0,5.0)

You should see that each of these return a floating point number. This is because division / with any other number returns a floating point.

Multiple Return Values

A very nice feature of Julia functions is that of multiple return values. Instead of only being able to return a single number (or requiring to send an array or structural type), you can return more than 1 number (or other data type). For example.

h(x,y) = x+y,x-y

and we call this in the same manner. For example,

h(3,5)

We can store the results of any function that returns multiple arguments in the following example:

p,q = h(3,5)

the p will take on the value 8 and q will take on the value of -2.

The result of this function is a tuple as we saw in section XXXX. Although in that section we used parentheses around the tuple, it is not necessary and generally isn’t used to return a tuple in a function. We will use this for the result of the quadratic formula in Chapter XXXX.