问题
I am working with a dataframe that has 65 variables in it. The first variable catalogs a person, and the next 64 variables indicate the geographic distance that person is from each of 64 locations. Using R, I would like to create a new variable that catalogs the shortest distance for each person to one of those 64 locations.
For example: if person X is 35, 50, 79, 100, 450...miles away from the locations, I would like the new variable to automatically assign them a 35, because this is the shortest distance. Any help with this would be much appreciated. Thanks.
回答1:
df <- data.frame(let=letters[1:25], d1=sample(1:25,25), d2=sample(1:25,25), d3=sample(1:25,25))
df$shortest <- apply(df[,2:4],1,min)
The second line applies the function min to each row and assigns it to the new column in my data.frame df. See ?apply for more explanation of what the second line is doing. Careful to skip the first column, or any columns that aren't distances:
apply(df,1,min) gives completely difference answers since its finding the "min" of strings.
> min(2:10)
[1] 2
> min(as.character(2:10))
[1] "10"
回答2:
Or, using the example of Justin:
df$shortest <- do.call(pmin,df[-1])
see also ?pmin and ?do.call, and note that you can drop the first variable in your data frame by using the list indices (so not using any comma at all, see also ?Extract )
回答3:
I'd approach this with apply but transform or other approach could work.
#fake data set
ID=LETTERS[1:5], distance=matrixsample(
DF <- as.data.frame(matrix(sample(1:100, rep=T, 100), 5, 20))
DF <- data.frame(ID=LETTERS[1:5], DF)
#solution
DF$newvar <- apply(DF[,-1], 1, min)
来源：https://stackoverflow.com/questions/8989900/getting-the-minimum-of-the-rows-in-a-data-frame