I was trying to compute the median of a given vector, but when I tried I kept on getting an error:
median(returns)
Error in median.default(returns) : need numeric data
> returns
[1] 0.001262733 -0.005048584 -0.009160197 0.010411955 -0.00542421
[6] -0.010982649 -0.005807832 0.000863131 -0.00210823 0.000117543
[11] 0.001319904 0.005307534 0.005246006 0.008469327 0.006006664
[16] -0.001411188 -0.011446652 0.002669714 0.003896259 -0.003060607
[21] 0.006306116 0.000895311 -0.006235211 -0.000856819 -0.00056599
[26] 0.00808345 0.00038652 -0.004070623 0.008398158 -0.005976036
[31] 0.011270873 0.007959499 0.003776885 -0.000591663 0.001163452
[36] 0.005759682 0.000678132 0.000609123 -0.000735042
40 Levels: -0.00056599 -0.000591663 -0.000735042 -0.000856819 ... 0.011270873
dput(returns)
structure(c(25L, 9L, 14L, 39L, 10L, 15L, 11L, 22L, 6L, 18L, 26L,
31L, 30L, 38L, 33L, 5L, 16L, 27L, 29L, 7L, 34L, 23L, 13L, 4L,
1L, 36L, 19L, 8L, 37L, 12L, 40L, 35L, 28L, 2L, 24L, 32L, 21L,
20L, 3L), .Label = c("-0.00056599", "-0.000591663", "-0.000735042",
"-0.000856819", "-0.001411188", "-0.00210823", "-0.003060607",
"-0.004070623", "-0.005048584", "-0.00542421", "-0.005807832",
"-0.005976036", "-0.006235211", "-0.009160197", "-0.010982649",
"-0.011446652", "#DIV/0!", "0.000117543", "0.00038652", "0.000609123",
"0.000678132", "0.000863131", "0.000895311", "0.001163452", "0.001262733",
"0.001319904", "0.002669714", "0.003776885", "0.003896259", "0.005246006",
"0.005307534", "0.005759682", "0.006006664", "0.006306116", "0.007959499",
"0.00808345", "0.008398158", "0.008469327", "0.010411955", "0.011270873"
), class = "factor")
Since you're reading it from excel, R is looking at the "DIV#0" messages and considering your data to be categorical, as if it was data saying "Blue", "Green", "Hazel", etc. So when you're asking for median, R is thinking you're asking for the median of eye color, which would make no sense.
To turn a list of factors into numbers:
returns.numbers <- as.numeric(as.vector(returns))
median(returns.numbers)