mutate( ) returns a matrix-CodePudding

After I update my Rstudio today, when I tried to get z-scores of a data frame by using mutate() and scale(), it returns a matrix with a 'new name' warning:

df <- df %>% group_by(participants) %>% mutate(zscore=scale(answer))

New names:

NA -> ...8

class(df$zscore)

[1] "matrix" "array"

The column of the z-scores should have been named 'zscore', but why it is now named '...8'? I never had any problems with the codes before. Is it because of the update?

CodePudding user response：

I think you just added another column without a header or read in data with a column without a header. There is no issue with your classes.

library(tidyverse)

test <- mtcars|>
  group_by(cyl) |>
  mutate(zscore=scale(mpg)) 

#class of test
class(test)
#> [1] "grouped_df" "tbl_df"     "tbl"        "data.frame"

#class of column
class(test$zscore)
#> [1] "matrix" "array"

#recreate warning
test <- test |>
  bind_cols("")
#> New names:
#> * `` -> `...13`

The warning at the bottom means that I added a column without a name in the 13th position.

CodePudding user response：

Part of the issue is that scale() returns a matrix. You can fix this by wrapping in as.double():

library(dplyr)

starwars2 <- starwars %>%
  select(height, gender) %>%
  group_by(gender) %>%
  mutate(zscore = as.double(scale(height)))

Output:

# A tibble: 87 × 3
# Groups:   gender [3]
   height gender     zscore
    <int> <chr>       <dbl>
 1    172 masculine -0.120 
 2    167 masculine -0.253 
 3     96 masculine -2.14  
 4    202 masculine  0.677 
 5    150 feminine  -0.624 
 6    178 masculine  0.0394
 7    165 feminine   0.0133
 8     97 masculine -2.11  
 9    183 masculine  0.172 
10    182 masculine  0.146 
# … with 77 more rows

But I’m not sure this explains your NA -> ...8 issue. If not, please update your question to include your data (using dput(df)) or a subset (using dput(head(df))).