How to convert a factor to integer\numeric without loss of information?

See the Warning section of ?factor:

In particular, as.numeric applied to a factor is meaningless, and may happen by implicit coercion. To transform a factor f to approximately its original numeric values, as.numeric(levels(f))[f] is recommended and slightly more efficient than as.numeric(as.character(f)).

The FAQ on R has similar advice.

Why is as.numeric(levels(f))[f] more efficent than as.numeric(as.character(f))?

as.numeric(as.character(f)) is effectively as.numeric(levels(f)[f]), so you are performing the conversion to numeric on length(x) values, rather than on nlevels(x) values. The speed difference will be most apparent for long vectors with few levels. If the values are mostly unique, there won’t be much difference in speed. However you do the conversion, this operation is unlikely to be the bottleneck in your code, so don’t worry too much about it.

Some timings

library(microbenchmark)
microbenchmark(
  as.numeric(levels(f))[f],
  as.numeric(levels(f)[f]),
  as.numeric(as.character(f)),
  paste0(x),
  paste(x),
  times = 1e5
)
## Unit: microseconds
##                         expr   min    lq      mean median     uq      max neval
##     as.numeric(levels(f))[f] 3.982 5.120  6.088624  5.405  5.974 1981.418 1e+05
##     as.numeric(levels(f)[f]) 5.973 7.111  8.352032  7.396  8.250 4256.380 1e+05
##  as.numeric(as.character(f)) 6.827 8.249  9.628264  8.534  9.671 1983.694 1e+05
##                    paste0(x) 7.964 9.387 11.026351  9.956 10.810 2911.257 1e+05
##                     paste(x) 7.965 9.387 11.127308  9.956 11.093 2419.458 1e+05

Related Posts:

  1. R Hex to RGB converter
  2. Error in file(file, “rt”) : cannot open the connection [duplicate]
  3. Error in : object of type ‘closure’ is not subsettable
  4. Could not find function “%<>%” with dplyr loaded
  5. Interpreting “condition has length > 1” warning from `if` function
  6. How to coerce a list object to type ‘double’
  7. R Error in x$ed : $ operator is invalid for atomic vectors
  8. $ operator is invalid for atomic vectors for dataframe R
  9. Plotting with ggplot2: “Error: Discrete value supplied to continuous scale” on categorical y-axis
  10. ggplot2 error : Discrete value supplied to continuous scale
  11. ggplot2 line chart gives “geom_path: Each group consist of only one observation. Do you need to adjust the group aesthetic?”
  12. ggplot2 line chart gives “geom_path: Each group consist of only one observation. Do you need to adjust the group aesthetic?”
  13. How to open CSV file in R when R says “no such file or directory”?
  14. Error: could not find function “%>%”
  15. R programming: How do I get Euler’s number?
  16. ‘x’ and ‘y’ lengths differ ERROR when plotting
  17. What are the “standard unambiguous date” formats for string-to-date conversion in R?
  18. ‘x’ and ‘y’ lengths differ ERROR when plotting
  19. What are the “standard unambiguous date” formats for string-to-date conversion in R?
  20. Difference between paste() and paste0()
  21. Remove duplicated rows
  22. Error in ggplot.data.frame : Mapping should be created with aes or aes_string
  23. Error in Confusion Matrix : the data and reference factors must have the same number of levels
  24. Error in plot.window(…) : need finite ‘xlim’ values
  25. Error in colMeans(x, na.rm = TRUE) : ‘x’ must be numeric, What should I do in this situation?
  26. Editing legend (text) labels in ggplot
  27. case_when in mutate pipe
  28. Principal Components Analysis:Error in colMeans(x, na.rm = TRUE) : ‘x’ must be numeric
  29. dim(X) must have a positive length when applying function in data frame
  30. Extract year from date
  31. Persistent invalid graphics state error when using ggplot2
  32. incorrect number of dimensions and incorrect number of subscripts in array
  33. What does %*% mean in R [duplicate]
  34. Why am I getting “algorithm did not converge” and “fitted prob numerically 0 or 1” warnings with glm?
  35. How to debug “contrasts can be applied only to factors with 2 or more levels” error?
  36. Error in lm.fit(x, y, offset = offset, singular.ok = singular.ok, …) : NA/NaN/Inf in ‘y’, tried every possible way
  37. R t-test Grouping factor must have exactly 2 levels error
  38. What does c do in R?
  39. Opposite of %in%: exclude rows with values specified in a vector
  40. Understanding the order() function
  41. Subscript out of bounds – general definition and solution?
  42. Error in lis[[i]] : attempt to select less than one element
  43. Plot a line graph, error in xy.coords(x, y, xlabel, ylabel, log) : ‘x’ and ‘y’ lengths differ
  44. How to compute weighted mean in R?
  45. Error: unexpected symbol/input/string constant/numeric constant/SPECIAL in my code
  46. How to count the number of observations in R like Stata command count
  47. Remove all of x axis labels in ggplot
  48. Sum rows in data.frame or matrix
  49. Error in table “all arguments must have the same length”
  50. Rename multiple columns by names
  51. What is the difference between rm() and rm(list=ls())?
  52. Remove rows with all or some NAs (missing values) in data.frame
  53. How to not run an example using roxygen2?
  54. Error with apply function
  55. How do you create vectors with specific intervals in R?
  56. Linear model function lm() error: NA/NaN/Inf in foreign function call (arg 1)
  57. Increase number of axis ticks
  58. Converting data frame column from character to numeric
  59. How to assign colors to categorical variables in ggplot2 that have stable mapping?
  60. Singularity in backsolve at level 0, block 1 in LME model
  61. “installation of package ‘FILE_PATH’ had non-zero exit status” in R
  62. Is there a dictionary functionality in R
  63. Plot two graphs in same plot in R
  64. reshape2 melt warning message
  65. ggplot2 manually specifying colour with geom_line
  66. dcast warning: ‘Aggregation function missing: defaulting to length’
  67. remove all variables except functions
  68. How to update a package in R?
  69. Run R script from command line
  70. Non-conformable arrays error in code
  71. What causes an R script to get Killed?
  72. What’s the difference between facet_wrap() and facet_grid() in ggplot2?
  73. ggplot2, facet_grid, free scales?
  74. dplyr mutate with conditional values
  75. How do I install an R package from source?
  76. How can I convert Json to data frame in R
  77. lmer error: grouping factor must be < number of observations
  78. R Error (from NA’s to 0): duplicate subscripts for column in Data Frame
  79. incorrect number of subscripts on matrix in R
  80. Error in rbind(deparse.level, …) : numbers of columns of arguments do not match R
  81. Creating box plot on exercise
  82. What is the meaning of the dollar sign “$” in R function()?
  83. How to sort a data frame by alphabetic order of a character variable in R?
  84. Error in na.fail.default(as.ts(x)) : missing values in object in time series forecasting
  85. Argument “No” is missing, with no default
  86. R apply function with multiple parameters
  87. Geometric Mean: is there a built-in?
  88. Error in na.fail.default: missing values in object – but no missing values
  89. Error: Invalid number of ‘breaks’ in R
  90. Convert the values in a column into row names in an existing data frame
  91. Deleting rows that are duplicated in one column based on the conditions of another column
  92. Replace all 0 values to NA
  93. The difference between bracket [ ] and double bracket [[ ]] for accessing the elements of a list or dataframe
  94. Merge error : negative length vectors are not allowed
  95. Error Error in storage.mode(x) <- "double" : 'list' object cannot be coerced to type 'double'
  96. why nrow(dataframe) and length(dataframe) in r give different results?
  97. Meaning of objects being masked by the global environment
  98. Subset and ggplot2
  99. Create a matrix of scatterplots (pairs() equivalent) in ggplot2
  100. cbind warnings : row names were found from a short variable and have been discarded

Leave a Comment

tech