How to create a new variable in a data frame based on a condition

Question

Assume we have a dataframe   x   y 1   1 2   4  4   5    how can you add a new variable to the dataframe such that if x is less than or equal to 1 it returns  good  if x is between 3 and 5 it returns  bad  else returns  fair   x   y  w 1   1   good  2   2    fair  5   5    bad    Applied the method shown by ocram   however this one here does not work    d1  lt - c  e    c    a   d2  lt - c  e    a    b    w  lt - ifelse d1     e   amp   d2   e    1  ifelse  d1     a    amp   d2    b    2  ifelse d1     e   3 99     Any ideas  Thanks

User · Answer

If you have a very limited number of levels  you could try converting y into factor and change its levels    gt  xy  lt - data frame x   c 1  2  4   y   c 1  4  5    gt  xy w  lt - as factor xy y   gt  levels xy w   lt - c  good    fair    bad    gt  xy   x y    w 1 1 1 good 2 2 4 fair 3 4 5  bad

User · Answer

One obvious and straightforward possibility is to use  if-else conditions   In that example  x  lt - c 1  2  4  y  lt - c 1  4  5  w  lt - ifelse x  lt   1   good   ifelse  x  gt   3   amp   x  lt   5    bad    fair    data frame x  y  w       For the additional question in the edit   Is that what you expect     gt  d1  lt - c  e    c    a    gt  d2  lt - c  e    a    b    gt    gt  w  lt - ifelse  d1     e    amp   d2     e    1        ifelse  d1   a    amp   d2     b    2       ifelse  d1     e    3  99     gt        gt  data frame d1  d2  w    d1 d2  w 1  e  e  1 2  c  a 99 3  a  b  2   If you do not feel comfortable with the ifelse function  you can also work with the if and else statements for such applications

[r] How to create a new variable in a data.frame based on a condition?

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