Changing values in a matrix depending on whether they are above of below a certain threshold value

问题

I have a matrix. If an element of the matrix is greater than 400, then I would like the element to become zero. If an element of the matrix is less than 400, then I would like to multiply the element by three.

Here is how to reproduce my matrix:

structure(c(122, 948, 952, 100,
942, 150, 150, 149, 
244, 220, 437, 395, 
356, 473, 434, 335, 
357, 371, 590, 553, 
520, 491, 426, 426, 
427, 177, 284, 338, 
391, 290, 345, 399, 
143, 193, 136, 121, 
122, 187, 177, 544), .Dim = c(10L, 4L), units = structure(list(
    numerator = "m", denominator = character(0)), class = "symbolic_units"), class = "units")

回答1:

With Matrix being your data:

for(i in 1:dim(Matrix)[2])
{
  Matrix[,i] <- ifelse(Matrix[,i]>400,0,
                       ifelse(Matrix[,i]<400,3*Matrix[,i],Matrix[,i]))
}

      [,1] [,2] [,3] [,4]
 [1,]  366    0    0 1035
 [2,]    0 1185    0 1197
 [3,]    0 1068    0  429
 [4,]  300    0    0  579
 [5,]    0    0    0  408
 [6,]  450 1005  531  363
 [7,]  450 1071  852  366
 [8,]  447 1113 1014  561
 [9,]  732    0 1173  531
[10,]  660    0  870    0

来源：https://stackoverflow.com/questions/63117901/changing-values-in-a-matrix-depending-on-whether-they-are-above-of-below-a-certa