R dplyr - spreading frequencies of grouping by month

Question

I would like to group my df by month and year. The outcome should be counted, frequencies for 0 and 1. I can get the overall frequencies but can't spread it. The issue is the last line of code. I get the error message at the bottom.

id <- 1:1000
outcome <- rbinom(1000, 1, 0.23)
date <- sample(seq(as.Date('2000/01/01'), as.Date('2002/12/31'), by="day"), 1000)
df <- data.frame(id, date, outcome)

library(dplyr)
library(tidyr)

df_month<- df%>%
    mutate(month = format(date, "%m"), year = format(date, "%Y")) %>%
    group_by(month, year) %>%
    summarise(freq = n())%>%
    spread(outcome, freq)

Error: var must evaluate to a single number or a column name, not an integer vector

Answer 1

I think this is what you need -

df_month <- df %>%
  mutate(month = format(date, "%m"), year = format(date, "%Y")) %>%
  group_by(month, year, outcome = paste0("outcome_", outcome)) %>%
  summarise(freq = n()) %>%
  spread(outcome, freq)

# A tibble: 36 x 4
# Groups:   month, year [36]
   month year  outcome_0 outcome_1
   <chr> <chr>     <int>     <int>
 1 01    2000         18        10
 2 01    2001         22         3
 3 01    2002         22         6
 4 02    2000         20         8
 5 02    2001         21         4
 6 02    2002         22         5
 7 03    2000         20         9
 8 03    2001         24         5
 9 03    2002         26         3
10 04    2000         19         9
# ... with 26 more rows