Generate a dummy-variable

Question

I have trouble generating the following dummy-variables in R:

I\'m analyzing yearly time series data (time period 1948-2009). I have two questions:

1. <

Answer 1

If you want to get K dummy variables, instead of K-1, try:

dummies = table(1:length(year),as.factor(year))  

Best,

Answer 2

I read this on the kaggle forum:

#Generate example dataframe with character column
example <- as.data.frame(c("A", "A", "B", "F", "C", "G", "C", "D", "E", "F"))
names(example) <- "strcol"

#For every unique value in the string column, create a new 1/0 column
#This is what Factors do "under-the-hood" automatically when passed to function requiring numeric data
for(level in unique(example$strcol)){
  example[paste("dummy", level, sep = "_")] <- ifelse(example$strcol == level, 1, 0)
}

Answer 3

Convert your data to a data.table and use set by reference and row filtering

library(data.table)

dt <- as.data.table(your.dataframe.or.whatever)
dt[, is.1957 := 0]
dt[year == 1957, is.1957 := 1]

Proof-of-concept toy example:

library(data.table)

dt <- as.data.table(cbind(c(1, 1, 1), c(2, 2, 3)))
dt[, is.3 := 0]
dt[V2 == 3, is.3 := 1]

Answer 4

I use such a function (for data.table):

# Ta funkcja dla obiektu data.table i zmiennej var.name typu factor tworzy dummy variables o nazwach "var.name: (level1)"
factorToDummy <- function(dtable, var.name){
  stopifnot(is.data.table(dtable))
  stopifnot(var.name %in% names(dtable))
  stopifnot(is.factor(dtable[, get(var.name)]))

  dtable[, paste0(var.name,": ",levels(get(var.name)))] -> new.names
  dtable[, (new.names) := transpose(lapply(get(var.name), FUN = function(x){x == levels(get(var.name))})) ]

  cat(paste("\nDodano zmienne dummy: ", paste0(new.names, collapse = ", ")))
}

Usage:

data <- data.table(data)
data[, x:= droplevels(x)]
factorToDummy(data, "x")

Answer 5

This one liner in base R

model.matrix( ~ iris$Species - 1)

gives

    iris$Speciessetosa iris$Speciesversicolor iris$Speciesvirginica
1                    1                      0                     0
2                    1                      0                     0
3                    1                      0                     0
4                    1                      0                     0
5                    1                      0                     0
6                    1                      0                     0
7                    1                      0                     0
8                    1                      0                     0
9                    1                      0                     0
10                   1                      0                     0
11                   1                      0                     0
12                   1                      0                     0
13                   1                      0                     0
14                   1                      0                     0
15                   1                      0                     0
16                   1                      0                     0
17                   1                      0                     0
18                   1                      0                     0
19                   1                      0                     0
20                   1                      0                     0
21                   1                      0                     0
22                   1                      0                     0
23                   1                      0                     0
24                   1                      0                     0
25                   1                      0                     0
26                   1                      0                     0
27                   1                      0                     0
28                   1                      0                     0
29                   1                      0                     0
30                   1                      0                     0
31                   1                      0                     0
32                   1                      0                     0
33                   1                      0                     0
34                   1                      0                     0
35                   1                      0                     0
36                   1                      0                     0
37                   1                      0                     0
38                   1                      0                     0
39                   1                      0                     0
40                   1                      0                     0
41                   1                      0                     0
42                   1                      0                     0
43                   1                      0                     0
44                   1                      0                     0
45                   1                      0                     0
46                   1                      0                     0
47                   1                      0                     0
48                   1                      0                     0
49                   1                      0                     0
50                   1                      0                     0
51                   0                      1                     0
52                   0                      1                     0
53                   0                      1                     0
54                   0                      1                     0
55                   0                      1                     0
56                   0                      1                     0
57                   0                      1                     0
58                   0                      1                     0
59                   0                      1                     0
60                   0                      1                     0
61                   0                      1                     0
62                   0                      1                     0
63                   0                      1                     0
64                   0                      1                     0
65                   0                      1                     0
66                   0                      1                     0
67                   0                      1                     0
68                   0                      1                     0
69                   0                      1                     0
70                   0                      1                     0
71                   0                      1                     0
72                   0                      1                     0
73                   0                      1                     0
74                   0                      1                     0
75                   0                      1                     0
76                   0                      1                     0
77                   0                      1                     0
78                   0                      1                     0
79                   0                      1                     0
80                   0                      1                     0
81                   0                      1                     0
82                   0                      1                     0
83                   0                      1                     0
84                   0                      1                     0
85                   0                      1                     0
86                   0                      1                     0
87                   0                      1                     0
88                   0                      1                     0
89                   0                      1                     0
90                   0                      1                     0
91                   0                      1                     0
92                   0                      1                     0
93                   0                      1                     0
94                   0                      1                     0
95                   0                      1                     0
96                   0                      1                     0
97                   0                      1                     0
98                   0                      1                     0
99                   0                      1                     0
100                  0                      1                     0
101                  0                      0                     1
102                  0                      0                     1
103                  0                      0                     1
104                  0                      0                     1
105                  0                      0                     1
106                  0                      0                     1
107                  0                      0                     1
108                  0                      0                     1
109                  0                      0                     1
110                  0                      0                     1
111                  0                      0                     1
112                  0                      0                     1
113                  0                      0                     1
114                  0                      0                     1
115                  0                      0                     1
116                  0                      0                     1
117                  0                      0                     1
118                  0                      0                     1
119                  0                      0                     1
120                  0                      0                     1
121                  0                      0                     1
122                  0                      0                     1
123                  0                      0                     1
124                  0                      0                     1
125                  0                      0                     1
126                  0                      0                     1
127                  0                      0                     1
128                  0                      0                     1
129                  0                      0                     1
130                  0                      0                     1
131                  0                      0                     1
132                  0                      0                     1
133                  0                      0                     1
134                  0                      0                     1
135                  0                      0                     1
136                  0                      0                     1
137                  0                      0                     1
138                  0                      0                     1
139                  0                      0                     1
140                  0                      0                     1
141                  0                      0                     1
142                  0                      0                     1
143                  0                      0                     1
144                  0                      0                     1
145                  0                      0                     1
146                  0                      0                     1
147                  0                      0                     1
148                  0                      0                     1
149                  0                      0                     1
150                  0                      0                     1

Answer 6

The simplest way to produce these dummy variables is something like the following:

> print(year)
[1] 1956 1957 1957 1958 1958 1959
> dummy <- as.numeric(year == 1957)
> print(dummy)
[1] 0 1 1 0 0 0
> dummy2 <- as.numeric(year >= 1957)
> print(dummy2)
[1] 0 1 1 1 1 1

More generally, you can use ifelse to choose between two values depending on a condition. So if instead of a 0-1 dummy variable, for some reason you wanted to use, say, 4 and 7, you could use ifelse(year == 1957, 4, 7).