R: Writing values into matrix according to x & y coordinates given-CodePudding

Hello everyone out here! I have a 63x6 matrix mat (Columns: x-coordinates, y-coordinates, value_1,value_2, etc). The value_1 should be written into a 7x9 matrix according to its coordinates given. This solution doesn't work: (like many others I've tried..)

for (r in 1:nrow(df))   {
    for (c in 1:ncol(df))  {
      df[r,c] <- mat$value_1[mat$x == c && mat$y == r]   
 
    }
}

Could anyone help? Thanks!

@Mael: I dont know if you meant it that way:

NMIN_struct <-
  structure(
    list(
      x = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 1),
      y = c(1,
            1, 1, 1, 1, 1, 1, 1, 1, 2),
      Sample_ID = c(1, 1, 1, 2, 2, 2, 3,
                    3, 3, 4),
      Nmin1 = c(
        11.1788110878291,
        11.1788110878291,
        11.1788110878291,
        5.17227718787078,
        5.17227718787078,
        5.17227718787078,
        5.39282332521486,
        5.39282332521486,
        5.39282332521486,
        2.76320633985937
      ),
      Nmin2 = c(
        2.16160208812242,
        2.16160208812242,
        2.16160208812242,
        1.89355337232599,
        1.89355337232599,
        1.89355337232599,
        1.82901181814765,
        1.82901181814765,
        1.82901181814765,
        1.37989208438326
      ),
      Nmin3 = c(
        1.01043537292747,
        1.01043537292747,
        1.01043537292747,
        1.05972539906962,
        1.05972539906962,
        1.05972539906962,
        0.901859608440133,
        0.901859608440133,
        0.901859608440133,
        0.710021005623553
      )
    ),
    row.names = c(NA,-10L),
    class = c("tbl_df", "tbl", "data.frame")
  )

CodePudding user response：

The base [ primitive accepts a 2-column matrix as an argument, where column 1 identifies rows and column 2 identifies columns. For instance, using a contrived matrix re-assigning 4 values in mtcars:

mat <- data.frame(row=c(1:3,3), col=c(2,3,1,3), val=90000:90003)

head(mtcars)
#                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
# Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
# Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
# Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
# Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
# Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
# Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

mtcars[ as.matrix(mat[,c("row","col")]) ] <- mat$val
head(mtcars)
#                       mpg   cyl  disp  hp drat    wt  qsec vs am gear carb
# Mazda RX4            21.0 90000   160 110 3.90 2.620 16.46  0  1    4    4
# Mazda RX4 Wag        21.0     6 90001 110 3.90 2.875 17.02  0  1    4    4
# Datsun 710        90002.0     4 90003  93 3.85 2.320 18.61  1  1    4    1
# Hornet 4 Drive       21.4     6   258 110 3.08 3.215 19.44  1  0    3    1
# Hornet Sportabout    18.7     8   360 175 3.15 3.440 17.02  0  0    3    2
# Valiant              18.1     6   225 105 2.76 3.460 20.22  1  0    3    1

(This works on frames and matrices alike.)