Selecting elements from objects

R For SAS Users

Melinda Higgins, PhD

Research Professor/Senior Biostatistician Emory University

Select element from vector

# Select 3rd element from x using []
x <- c(5,3,2)
x[3]

Result

column vector with three numbers 5 3 2

# Select value at row 1 column 2
m[1, 2]

Result

4.1

matrix with 2 columns 3 rows

# Leave row blank, select column 2
m[, 2]

Result

     4.1 2.2 5.4

select column 2 from matrix

# Select row 3, leave column blank
m[3, ]

Result

     2.4 5.4

select row 3 from matrix

# Select element at row 2 column 3
d[2, 3]

     FALSE

# Select second column from d
d[, 2]

     child young old

# Select third row from d
d[3, ]

     2.4 old TRUE

data frame with 3 columns score age and test

# Select test variable from d
d[,"test"]

Result

[1]  TRUE FALSE TRUE

data frame with 3 columns score age and test

# Use pull() get test column
d %>% pull(test)

Result

     TRUE FALSE TRUE

pull column test from data frame

# Use select(), get age and test
d %>% select(age:test)

# Extract test and score from d
d %>% select(test, score)

    age  test
1 child  TRUE
2 young FALSE
3   old  TRUE

   test score
1  TRUE   5.0
2 FALSE   3.1
3  TRUE   2.4

# Use slice(), get rows 2 through 3
d %>% slice(2:3)

Result

     score   age  test
       3.1 young FALSE
       2.4   old  TRUE

slice 2 rows from data frame

# View d
d

# Extract row 2 from d
d %>% slice(2)

# Extract rows 3 and 1 from d
d %>% slice(c(3,1))

  score   age  test
1   5.0 child  TRUE
2   3.1 young FALSE
3   2.4   old  TRUE

  score   age  test
1   3.1 young FALSE

  score   age test
1   2.4   old TRUE
2   5.0 child TRUE

R For SAS Users