Question

Possible Duplicate:
Assigning values to a df$column based on another column in the same df

Suppose I have the data frame:

table<- data.frame(population=c(100, 300, 5000, 2000, 900, 2500), habitat=c(1,2,3,4,5,6))

Now I want to add a new column table$size with the values 1 if population< 500, 2 if 500<=population<1000, 3 if 1000<=population<2000, 4 if 2000<=population<3000, 5 if 3000<=population<=5000

I only know how to create a column with a binary TRUE/FALSE outcome conditional on the values in another column , e.g.

table$size <- (table$population<1000) 

But I’m not sure to do it to get different numbers for different conditions. Can anyone provide help on this?

Answer 1

First of all don’t call a data.frame table, because table is a base function.

You can use findInterval:

df <- data.frame(population=c(100, 300, 5000, 2000, 900, 2500), 
                 habitat=c(1,2,3,4,5,6))
v <- c(-Inf,500,1000,2000,3000,5000)
df$size <- findInterval(df$population,v,all.inside = TRUE)
  population habitat size
1        100       1    1
2        300       2    1
3       5000       3    5
4       2000       4    4
5        900       5    2
6       2500       6    4

I used all.inside = TRUE since you wanted to define 5000 as size 5 and I assume values cannot be greater than that. If they can, you could use something like

v <- c(-Inf,500,1000,2000,3000,5001,Inf).