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R function: seq

by=4

Create a vector, starting with 20, incrementing by 4, with greatest element not greater than 41:

seq(20, 41, by=4)
# [1] 20 24 28 32 36 40

Github repository about-r, path: /functions/seq/by.R

length=4

Create exactly 4 elements between 10 and 26, inclusively:

seq(10, 26, length=4)
# [1] 10.00000 15.33333 20.66667 26.00000

Github repository about-r, path: /functions/seq/length.R

Creating a sequence of dates

When starting with a »date« value such as created by ISODate(…), seq creates a vector of dates.

The by parameter then understands durations such as week:

seq(from       = ISOdate(2016, 8, 28),
    by         ="week"  , # Dates are a week apart
    length.out = 5)
# [1] "2016-08-28 12:00:00 GMT" "2016-09-04 12:00:00 GMT"
# [3] "2016-09-11 12:00:00 GMT" "2016-09-18 12:00:00 GMT"
# [5] "2016-09-25 12:00:00 GMT"

Github repository about-r, path: /functions/seq/date.R

Using seq to plot an x/y function

First seq(…) is used to fill x values to a vector (named x). Then, a vector, named y, is filled by calling a function.

Finally, x and y are ploted;

x11(width=5,height=3)

x <- seq(0, 30, by=.1)
y <- exp(-x*0.2) * sin(x)

# png(file = 'img/x-y-plot.png', width=300, height=180)
par(mar=c(2, 2, 0.1, 0.1))
plot(x, y, type='l')
# dev.off()

# Wait for mouse click or enter pressed
z <- locator(1)

Github repository about-r, path: /functions/seq/x-y-plot.R

Misc

»Parameter along«

df <- data.frame(
  col_1 = c(   1 ,    2 ,    3 ,    4 ,    5 ,    6 ,    7 ,    8 ),
  col_2 = c('Foo', 'Foo', 'Bar', 'Foo', 'Baz', 'Baz', 'Foo', 'Bar')
)
df.splitted <- split(df, 
          c(  'A',   'A',   'A',   'B',   'A',   'B',   'C',   'C')
)

df.splitted
seq(along=df.splitted)
# [1] 1 2 3

Github repository about-r, path: /functions/seq.R