03_using_scripts.qmd

# Using Scripts

Until now, we have submitted each command to **[R]{.sans-serif}** by
typing directly at the command prompt. In almost all situations, it is
**much** better to type code in a separate file called a script file.
There are many advantages of using script files.

-   Repeatability

-   Editing

-   Submitting many commands at once

## Scripts in **[R]{.sans-serif}** GUI

To open an **[R]{.sans-serif}** script, go to File `->` New Script. You
can type your commands in the resulting windows. It is useful to save
your script files with a .R extension. Then the operating system
recognizes this as an **[R]{.sans-serif}** file.

After opening a new script, type

`> history()`

A new window will open with the last 25 commands you have used. You can
get a longer history with, say,

`> history(100)`

Select all your commands and copy-paste them to the new script. Save the
file with a .R extension.

There are several ways of submitting commands from the
**[R]{.sans-serif}** script window.

-   Copy and Paste from the script window to the interpreter window

-   Control-r

-   The `source` command. If your file is saved as *myfile.R*, you can
    run all the commands in the file by typing the following line at the
    command prompt.

    `> source("myfile.R")`

    In order for **[R]{.sans-serif}** to read your script, you must use
    the full path or be in the correct working directory. To change the
    current working directory, go to File `->` Change Dir, then browse
    to the appropriate folder.

    To see the files in the current working directory, type:

    `> dir()`

    Another possibility is to find the file using

    `> source(file.choose())`

    but this does not change the working directory.

## Comments

Documentation and formatting are essential to writing effective
**[R]{.sans-serif}** code. If you come back to a project after a few
months (days? hours?), you want to know what the code is doing without
retracing every single step. Comments in **[R]{.sans-serif}** can be
inserted with the `#` symbol. **[R]{.sans-serif}** will not process the
rest of the line after the `#`.

`> 5 < 6`

`> 5 # < 6`

The following is an example of a commented **[R]{.sans-serif}** script.
Some of the functions we have used before; others will be explained
later. Let's open it in **[R]{.sans-serif}**Studio and see what it does.

## **[R]{.sans-serif}**Studio

**[R]{.sans-serif}**Studio is an interface to **[R]{.sans-serif}**. It
organizes the user's screen into windows that display programs
(scripts), objects, graphics, and the **[R]{.sans-serif}** interpreter.
Launch **[R]{.sans-serif}**Studio from the start menu. Click on the
folder in the upper left corner and browse to the folder containing the
script "sample script.R". The following should open in the upper left
window.

## Sample Script

\# sample script.R

\# Chris Andrews

\# Created 2015 04 01

\# Last Modified 2019 02 03

\# This script analyzes the Life Cycle Savings data.

\# See help(LifeCycleSavings) for more details.

\#

\# Shorten the name and make local copy

Life = LifeCycleSavings

\# Examine Structure

head(Life)

dim(Life)

str(Life)

\# Descriptives

summary(Life)

\# Pairwise associations

cor(Life)

pairs(Life)

\# Fit a multiple regression model

mr.mod = lm(sr   pop15 + pop75 + dpi + ddpi, data=Life)

summary(mr.mod)

anova(mr.mod)

\# Plot the fit

par(mfrow=c(2,2), las=1, mar=c(4.5,4.5,2,1))

plot(mr.mod)

Use "Ctrl-Enter" to submit each line of the script. Take note of what
happens as each line is submitted to the interpreter.