dplyr: “Error in n(): function should not be called directly”

问题

I am attempting to reproduce one of the examples in the dplyr package but this error message. I am expecting to see a new column n produced with the frequency of each combination. Can someone tell me what I am missing? I triple checked that the package is loaded. Thanks for the help, as always.

 library(dplyr)
# summarise peels off a single layer of grouping
by_vs_am <- group_by(mtcars, vs, am)

by_vs <- summarise(by_vs_am, n = n())

Error in n() : This function should not be called directly

回答1:

I presume you have dplyr and plyr loaded in the same session. dplyr is not plyr. ddply is not a function in the dplyr package.

Both dplyr and plyr have the functions summarise/summarize.

Look at the results of conflicts() to see masked objects.

回答2:

As mentioned by the previous answer, you may have a conflict between plyr and dplyr. You can to run this command to unload the plyr package.

detach("package:plyr", unload=TRUE)

Then you can continue as expected.

library(dplyr) 
...
summarise(n = n())

回答3:

To avoid confusions with masking functions, it is clear to use the "package::function" specification, like example below:

delay <- dplyr::summarise(by_tailnum, 
  count = n(), 
  dist = mean(distance, na.rm = TRUE), 
  delay = mean(arr_delay, na.rm = TRUE))

回答4:

In another case, this error occurred in the following code.

library(dplyr) # dplyr 0.5.0
library(lazyeval)

df <- data_frame(group = c(1, 2, 2, 3, 3, 3))

g <- "group"

df %>%
  group_by_(g) %>%
  summarise_(
    n = n(),
    sum = interp(~sum(col, na.rm = TRUE), col = as.name(g))
  )
# Error in n() : This function should not be called directly

It can be solved as follows.

df %>%
  group_by_(g) %>%
  summarise_(
    n = "n()",
    sum = interp(~sum(col, na.rm = TRUE), col = as.name(g))
  )
# A tibble: 3 × 3
# group     n   sum
# <dbl> <int> <dbl>
# 1     1     1     1
# 2     2     2     4
# 3     3     3     9

回答5:

Faced similar issue while executing code as per mentioned blog and then run solution in detach("package:plyr", unload=TRUE)

Blog : https://www.analyticsvidhya.com/blog/2017/09/comparative-stock-analysis/

Master_Data_AutoCorrelations<-Master_Data_lags %>%
  gather(key = "lag", value = "lag_value", -c(Stock,Date, Close)) %>%
  mutate(lag = str_sub(lag, start = 5) %>% as.numeric) %>%
  group_by(Stock, lag) %>%
  summarize(
    cor = cor(x = Close, y = lag_value, use = "pairwise.complete.obs"),
    cutoff_upper = 2/(n())^0.5,
    cutoff_lower = -2/(n())^0.5
  )

Post running detach,when above code was rerun it worked fine though received warning message as per below ,not sure whether plyr got unloaded or not.And how is the code executed properly ?

Warning message: ‘plyr’ namespace cannot be unloaded: namespace ‘plyr’ is imported by ‘reshape2’, ‘scales’, ‘broom’, ‘ggplot2’ so cannot be unloaded

回答6:

for me the solution was detach() function I utilized that function down package

来源：https://stackoverflow.com/questions/22801153/dplyr-error-in-n-function-should-not-be-called-directly

标签

function

plyr

dplyr

conflicting-libraries