查找与R中每一行的最小值对应的列名

Question

i have to extract column names corresponding to least 10 values for each row of a data frame and print it in new data frame.Can anyone help me do that?

my data frame looks like this:(15 x 15 matrix)

    > head(yt)
        V2   V3   V4   V5   V6   V7   V8   V9  V10  V11  V12  V13  V14  V15 
    1    0  966 1513 2964 1149  927 1611 1510  390  466 1820 1718  504 1179  
    2  966    0 2410 1520 1817  729  686  290 1823  168 2027  172 1610 1500 
    3 1513 2410    0  604  481 2742 1833  826  214 1618 1712  567  544 1313 
    4 2964 1520  604    0  595 1289 1446  466 1139  430  428  201  452 1574 
    5 1149 1817  481  595    0  494  550 2641  765  934 1813 1516  378 1363 
    6  927  729 2742 1289  494    0 1279 1197 2956  299  888  491 1408 1432

for each of the 15 rows i would like to know column names for least 10 columns

i know which.min gives least column name for each row but can you let me know other ways of computing least 10 values

Answer 1

The order function will give the ordering of a vector. So the first value of its result corresponds to the index of the smallest value in the vector. The second to the index of the second smallest etc. Using it in a function and using the apply function we can apply it to all rows. The apply function's result is column wise, which you probably don't want, so the transpose is taken over the result.

first_10 <- function(x) order(x)[1:10]
t(apply(dat, 1, first_10))