Extracting Columns from Data Frames as Vectors

Generally, a column in a data frame contains the values for a specific variable. Thus, we often wish to extract a column from a data frame as a vector of values so that we can work with it.

pers <- read.csv('https://faculty.ung.edu/rsinn/data/personality.csv')

Option 1: Dollar Sign Notation $

head

The R function head() displays the column titles and first few rows of a data frame. We often find it useful to inspect a compact version of a data frame instead of producing hundreds of rows in the display.

To extract the perfectionism scores column of data using the dollar sign method, we proceed as follows:

perfect <- pers$Perf
head(perfect, 5)

1. 105
2. 105
3. 73
4. 90
5. 95

Option 2: [Row, Column] Format

To extract the perfectionism scores column of data using the Rows and columns of the data frame, we leave the row indicator empty and specify a column as shown:

perfect2 <- pers[ , 'Perf']
head(perfect2, 5)

1. 105
2. 105
3. 73
4. 90
5. 95

The column may described either by number (shown below) or by name (as shown above). The perfectionism scores are stored in column #27.

perfect3 <- pers[ , 27]
head(perfect3, 5)

1. 105
2. 105
3. 73
4. 90
5. 95

All methods shown work properly and, as one can see, display identical results.

females <- subset(pers, Sex == 'F')
head(females, 5)

	Age	Yr	Sex	G21	Corps	Res	Greek	VarsAth	Honor	GPA	...	Perf	OCD	Play	Extro	Narc	HSAF	HSSE	HSAG	HSSD	PHS
2	20	3	F	N	N	2	Y	N	Y	3.95	...	105	3	172	16	11	46	52	26	33	SE
4	27	3	F	Y	N	3	N	N	N	2.84	...	90	9	160	16	10	51	51	23	19	SE
6	22	3	F	Y	N	2	Y	N	N	2.63	...	114	20	133	10	9	40	27	31	28	AG
8	20	3	F	N	N	1	Y	N	N	3.30	...	142	17	168	16	9	55	45	24	29	AF
9	22	2	F	Y	N	1	N	N	N	3.02	...	119	16	141	10	9	52	47	32	26	SE

data <- pers[ , 'Narc']

layout(matrix(c(1,2), ncol = 2), lcm(8))
hist(data)
plt <- { qqnorm(data, main = 'QQ Plot: Narcissism') ; qqline(data) }