MGSC 291 Walters Exam 1

Defining an Object

Stored objects

ls() or objects()

Check the class

class()

What does the class function return

numeric, integer, character, logical

How does R store categorical data

As a factor

How to assign data as a factor

_______

Combine function

c().... ex: >(vec1

How to check the data type

is.numeric() or is.atomic() or is.vector()

Defining vectors

is.character(c()) or is.vector(c())

Average

mean()

Equal to

==

not equal to

!=

less than

<

less than or equal to

greater than

>

Greater than or equal to

>=

Or

|

And

&

Standard Deviation

sd()

Sum function

sum(),The SUM Function adds all the numbers in a range of cells.

summary function

summary(), returns 5 # summary and mean for numerical data

Rounding function

round((variable),# of places)

If else function

(ifelse"variable"

Data structure and type

str()

Number of elements in a vector

length()

reading in the data

"name"

Finding working directory

getwd()

setting working directory

stewed()

what is strings=TRUE

If you want your character data to be read in as a factor (which is what we will almost always want), use strings=T in the read.csv call.

How to make data numeric

as.numeric()

subsetting

use brackets to specify which row or column you want to apply a function to

ex: variable(". "[subsetted variable])

what does na.rm=TRUE mean

Ignores the NAs in the data to give results for some functions

What is a parameter

number used to describe/summerize the population

Statistic

number calculated from a sample (used to estimate the parameter)

Observational Unit

the unit upon which an observation is made (rows of the dataset)

Variable

a characteristic of an individual or item in the population (columns in the dataset)

Quantitative

numbers that have magnitude (have a unit of measure)

Discrete

counted

Continuos

measured

Qualitive (categorical)

Non-numeric values, No magnitude (ex: zip code, area code, social security number)

nominal

variables that have value that can not be ordered (ex: undergraduate majors)

Ordinal

values can be ordered (ex: length of time employed,

Indentifier variable

a unique indetifier assigned to each individual or item in a group (don't have units, special kind of categorical data, not variables to be analyzed)

Time Series

Variable that is measured at regular intervals over time (sequence of data, equally spaced intervals[daily, weekely, monthly, etc...])

Cross sectional data

when a variable is measured on many subjects at the SAME point in time (or same time frame)

Panel Data

Multiple observational units measured over time (multiple time series overtime in a single dataset)

Data Lake

collection of structured, semi-structured, and unstructured data stored in a single location

Used by data engineers, data architects, and data scientists

data warehouse

stores structured data that is ready for data analytics

Used by business professionals that need ready data

Boxplot

displays the 5-number summary as a central box with whiskers that extend to the non-outlying data values

Code: >boxplot(Yvaraible~Xvariable)

Histogram

Displays the distribution of a quantitative variable. The horizontal axis is marked in the units of measurement for the variable. The vertical axis contains the scale of counts or percents. Each bar in the graph represents an equal-width class.

Code: >hist()

Scatterplot

a graphical depiction of the relationship between two variables

Code: > plot()

xlab

The X axis label

ylab

The y axis label

main

title

sub

subtitle

cex.lab

Font size for label annotation

cex.main

font size for title

line graph

Visualization of one of more time series

bar graph

Displaying categorical data ( a single number for each category, can display parts of a whole or sperate values, gaps between bars)

Pie Chart

categorical data, represents part of a whole

Sample mean

Balanncing point

code: >mean()

Sample median

the middle value in a series of measurements or observations, chosen so that there are equal numbers of measurements in the series that are larger than the median and smaller than the median

code: >median()

Skewed left

mean < median

-tail to the left

symmetric

mean = median

skewed right

mean > median

tail to the right

Mode

most frequently occurring score

Range

Distance between highest and lowest scores in a set of data.

code: >range()

IQR

Q3-Q1

code: >IQR()

variance

standard deviation squared

code: >var()

standard deviation

a measure of variability that describes an average distance of every score from the mean

code: sd()

For symmetric data, report the....

Mean and SD

For skewed distributions, report the....

Median and Quartiles

coefficient of variation

(standard deviation/ mean) X 100

code: >cv()

z-score

the number of standard deviations a particular score is from the mean

Z= (obs. - mean)/SD

Chebyshev's Theorem

for any data set, the proportion of observations that lie within k standard deviations from the mean is at least 1-1/k^2, where k is any number greater than 1 (at least)

2 75%

3 88.9%

4 93.8%

5 96%

Empirical Rule (68-95-99.7)

for datasets that are relatively symmetric/bell shaped

1 sd 68% of data

2 sd 95% of data

3 sd 99.7% of data

skewness

A measure of the shape of a data distribution. Data skewed to the left result in negative skewness; a symmetric data distribution results in zero skewness; and data skewed to the right result in positive skewness

Code: >skewness()

Kurtosis

Measure of the fatness of the tails of a probability distribution relative to that of a normal distribution. Indicates likelihood of extreme outcomes.

Excel uses 0 as a basline instead of 3

code: >kurtosis()

Risk to return

CV, sd/mean

higher the # more riskey

Return to risk

1/CV, mean/SD

Lower number more risky