Create an empty dataframe and append rows to it in R

Question

I have a dataframe from which I want to extract some rows that meet a condition. I am already able to succesfully get the index of those rows, but when I try to append those rows to the empty dataframe I've created I have all kinds of errors (or even funnier, no errors but an empty dataframe).

datosA <- read_excel(archivo, col_names = TRUE, sheet = "Sheet1")
datosB <- read_excel(archivo, col_names = TRUE, sheet = "Sheet1")

AvsB <- data.frame()

for (x in datosA$'m/z') {
  if (!(x %in% datosB$'m/z')) {
    index <- match(x, datosA$'m/z')
    rbind(AvsB, datosA[index,])
  }
}

Unfortunately this does nothing.

head(datosA)
# A tibble: 6 x 16
    Row Index `Peak Name`      `m/z` `Ret. Time`  `HC 1`  `HC 2` `QC 1` `FM 1`  `HC 3` `QC 2` `FM 2` `QC 3` `FM 3` `QC 4` `FM 4`
  <dbl> <dbl> <chr>            <dbl>       <dbl>   <dbl>   <dbl>  <dbl>  <dbl>   <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>
1     1     1 288.3/7.8 (80)    288.        7.82  82639  133150. 115280  32179  45842  116433  37358 138583  32425 217890  37055
2     2     2 288.3/8.0 (82)    288.        7.96  85895. 140309  119273  15051  63766  132999  12131 146485  13557 245226  14266
3     3     3 301.1/1.3 (92)    301.        1.28 141133. 161141. 180196  22494 168913  185736  26525 172954  29359 156029  25718
4     4     4 313.3/15.7 (99)   313.       15.7   92327. 116870   90781    816  84477. 126151    801 126316    971 186423    990
5     5     5 316.3/11.9 (104)  316.       11.9   12232.   8196.  10279    660  15646   15529    679  20439    657  17514    576
6     6     6 316.3/8.5 (105)   316.        8.47  98679  111867. 105794  62869  74714. 111100  77540 153424  80128 159846  76565

Answer 1

You need to store the result of rbind back into AvsB in each loop:

datosA <- read_excel(archivo, col_names = TRUE, sheet = "Sheet1")
datosB <- read_excel(archivo, col_names = TRUE, sheet = "Sheet1")

AvsB <- data.frame()

for (x in datosA$'m/z') {
  if (!(x %in% datosB$'m/z')) {
    index <- match(x, datosA$'m/z')
    AvsB <- rbind(AvsB, datosA[index,])
  }
}