How to convert data frame column from Factor to numeric

Question

I have a data frame whose class column is Factor  I d like to convert it to numeric so that I can use correlation matrix    gt  str breast   data frame     699 obs  of  10 variables           class                     Factor w  2 levels  2   4   1 1 1 1 1 2 1 1 1 1      gt  table breast class    2   4  458 241  gt  cor breast  Error in cor breast     x  must be numeric   How can I convert a Factor column to a numeric column

User · Answer

As an alternative to  dollarsign notation  use a within block   breast  lt - within breast      class  lt - as numeric as character class        Note that you want to convert your vector to a character before converting it to a numeric  Simply calling as numeric class  will not the ids corresponding to each factor level  1  2  rather than the levels themselves

User · Answer

From  factor      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

User · Answer

breast class  lt - as numeric as character breast class     If you have many columns to convert to numeric  indx  lt - sapply breast  is factor  breast indx   lt - lapply breast indx   function x  as numeric as character x      Another option is to use stringsAsFactors FALSE while reading the file using read table or read csv  Just in case  other options to create change columns    breast   class    lt - as numeric as character breast   class       or    breast  lt - transform breast  class as numeric as character breast

User · Answer

This is FAQ 7 10   Others have shown how to apply this to a single column in a data frame  or to multiple columns in a data frame   But this is really treating the symptom  not curing the cause   A better approach is to use the colClasses argument to read table and related functions to tell R that the column should be numeric so that it never creates a factor and creates numeric   This will put in NA for any values that do not convert to numeric   Another better option is to figure out why R does not recognize the column as numeric  usually a non numeric character somewhere in that column  and fix the original data so that it is read in properly without needing to create NAs   Best is a combination of the last 2  make sure the data is correct before reading it in and specify colClasses so R does not need to guess  this can speed up reading as well

[r] How to convert data.frame column from Factor to numeric

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