Psych10A quiz 2

dim(dat)

A function that helps you find the number of rows and columns in a dataset.

Boolean indexing

An indexing method that uses truth values (True/False) to filter data.

Wide data

Data format where each subject has one row, and different variables are stored in separate columns.

Long data

A data format where each row represents one observation of a single variable for a given subject.

Correlation

Statistical measure ranging from -1 to 1 indicating the strength and direction of a relationship between two variables.

round(cor(Dat),2)

A command to round correlation data to two decimal places.

R = 1

Indicates a perfect positive correlation between variables.

R = 0

Indicates no correlation between variables.

R = -1

Indicates a perfect negative correlation between variables.

tapply(score,group,mean)

A function used to compute the mean of 'score' grouped by 'group'.

Truth values

Values that can be either True or False, used in Boolean indexing.

Strings

Text values contained within quotation marks, including vector of strings.

dat[1:5,]

Indexing command in R to retrieve rows 1 to 5 from dataset 'dat'.

dat[1,0]

An incorrect data indexing command as it implies grabbing all from row one with a non-existent column.

To check that if there is missing data

we check whether the number of elements of score is the number of courses times the number of questions.

function for finding if there are any missing data

ncourse * nquestion == length(dat$score) if you get TRUE, than there are no missing data points

The function to find the output mean for each question in a data set

question_mean <- tapply(dat$score,dat$question,mean)

To make a filter for only searching for select scores of a data set

filterQ1 <- dat$question=="q1"

Function To make a filter for a select question

FilterQ1<- (dat$question=="q1")

q1scores<-(dat$score[FilterQ1])

print(q1scores)

To make a histogram

hist(q1scores)

abline(v=c1_q1scores)

what is the SEQ function used for?

used to generate sequences of numbers — similar to the : operator(from, to,by)