dplyr::n() returns “Error: Error: n() should only be called in a data context ”

Question

I got for the following code

for (i in c(1:(ncol(df_multi_paths_cols) - 1))) {

  df_cache <- df_multi_paths_cols %>%
    select(num_range(\"ord_\", c(         


        

Answer 1

This is because of the conflicts in packages, i.e., summarize/summarise is present in both the "dplyr" package and the "plyr" package. It is likely the function got called from the wrong package, resulting in this error. We can call the function while referencing its package to avoid such an issue.

To demonstrate:

# Call summarise from plyr library
plyr::summarise(count = n())

# Call summarise from dplyr library
dplyr::summarise(count = n())

I think this will help, let me know if you have any issue. Cheers.

Answer 2

The error disappeared by specifying for each function of the dplyr package the relative package of provenience:

for (i in c(1:(ncol(df_multi_paths_cols) - 1))) {

  df_cache <- df_multi_paths_cols %>%
    select(num_range("ord_", c(i, i+1)))   %>% 
    na.omit()  %>% 
    dplyr::group_by(.dots = c(paste0("ord_", c(i, i+1))))  %>% 
    dplyr::summarise(number=dplyr::n())  %>%
    ungroup() 

    colnames(df_cache)[c(1, 2)] <- c('channel_from', 'channel_to')
    df_res[[i]] <- df_cache
}

Pretty much now I think it was some kind of conflict with other packages with the same function name "summarise", as proved by

> conflicts()
  [1] "predictors"    "%>%"           "compact"       "lift"          "cols"          "%>%"          
  [7] "%>%"           "shift"         "take"          "transpose"     "%>%"           "add_row"      
 [13] "arrange"       "as_data_frame" "as_tibble"     "between"       "coalesce"      "count"        
 [19] "data_frame"    "data_frame_"   "desc"          "failwith"      "first"         "frame_data"   
 [25] "glimpse"       "id"            "last"          "lst"           "lst_"          "mutate"       
 [31] "n"             "rename"        "summarise"     "summarize"     "tbl_sum"       "tibble"       
 [37] "tribble"       "trunc_mat"     "type_sum"      "matches"       "%>%"           "%>%"          
 [43] "expand"        "expm"          "t"             "%>%"           "enexpr"        "enexprs"      
 [49] "enquo"         "enquos"        "ensym"         "ensyms"        "expr"          "quo"          
 [55] "quo_name"      "quos"          "sym"           "syms"          "vars"          "dcast"        
 [61] "melt"          "smiths"        "coerce"        "plot"          "print"         "show"         
 [67] "summary"       "t"             "cov"           "cov2cor"       "df"            "filter"       
 [73] "lag"           "lowess"        "predict"       "smooth"        "toeplitz"      "update"       
 [79] "var"           "image"         "plot"          "?"             "data"          "head"         
 [85] "tail"          "Arith"         "cbind2"        "coerce"        "Compare"       "kronecker"    
 [91] "Logic"         "Math"          "Math2"         "Ops"           "rbind2"        "show"         
 [97] "Summary"       "all.equal"     "as.array"      "as.matrix"     "body<-"        "chol"         
[103] "chol2inv"      "colMeans"      "colSums"       "crossprod"     "det"           "determinant"  
[109] "diag"          "diag<-"        "diff"          "drop"          "format"        "intersect"    
[115] "isSymmetric"   "kronecker"     "mean"          "norm"          "Position"      "print"        
[121] "qr"            "qr.coef"       "qr.fitted"     "qr.Q"          "qr.qty"        "qr.qy"        
[127] "qr.R"          "qr.resid"      "rcond"         "rowMeans"      "rownames"      "rowSums"      
[133] "setdiff"       "setequal"      "solve"         "summary"       "t"             "tcrossprod"   
[139] "union"         "unname"        "url"           "which"         "zapsmall"