I have a data frame of the following type:
Date X1 ....
2010-01-01 4
2010-01-02 5
2010-01-27 4
2012-03-10 2
...
So I am using the table() function to see the frequency of sampling each day/month. That means that I'm not looking at the values of each sampling, only it there is one that day. The thing is, I have generated an additional column called "season" using the "hydroTSM" package. So my idea is to use the following code:
df %>%
filter(date >= "2010-01-01") %>%
filter(date <= "2010-12-30") %>%
table(.$season)
But it gives me error.
Error in xtrm.data.frame(x) :cannot xtfrm data frames.
However if I save it as a "date" variable and then do "table(date$season)" I get what I wanted.
data <- df %>%
filter(date >= "2010-01-01") %>%
filter(date <= "2010-12-30") %>%
as.data.frame(df$date, df$season)
table(data$season)
Is it possible to do this with pipes?
While I would also use the exposition pipe, another option would be to use with.
library(magrittr)
mtcars %>%
with(table(cyl, gear))
The thing to understand is that %>% places the left hand side into the corresponding position of the right hand side (typically in the first slot).
Thus, mtcars %>% table(.$cyl) translates to table(mtcars, .$cyl) as you can easily verify:
trace(table, quote(print(list(...))))
# Tracing table(., .$cyl) on entry
# [[1]]
# mpg cyl disp hp drat wt qsec vs am gear carb
# Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
# Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
# Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
# Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
# Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
# Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
# Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
# Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
# Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
# Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
# Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
# Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
# Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
# Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
# Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
# Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
# Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
# Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
# Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
# Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
# Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
# Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
# AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
# Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
# Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
# Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
# Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
# Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
# Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
# Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
# Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
# Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
#
# [[2]]
# [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4
#
# Error in xtfrm.data.frame(x) :
# (converted from warning) cannot xtfrm data frames
That is, technically the term .$cyl is understood and properly evaluated, but tidyverse does not recognize it as it does with the single dot (i.e. use the LHS at this position and not in the first:
f <- function(a, b) print(list(a = a, b = b))
2 %>% f("a")
# $a
# [1] 2
# $b
# [1] "a"
# 2 %>% f("a", .)
# $a
# [1] "a"
# $b
# [1] 2
In the second case, tidyverse recognize the presence of . and thus does not add it again as the first argument.
The IMHO cleanest approach is to surround the RHS with curly braces like this, which overrides the default behavior of placing the dot in the first slot:
mtcars %>%
{ table(.$cyl, .$gear) }