使用一定范围的列（R）将函数应用于每一行

Question

My data contains consecutive columns V1-V1998 with other columns at either side of these. I want to calculate the skewness of the rows within this range of 1998 columns.

Here is the code I tried:

ND2a <- NoDup2 %>%
  rowwise() %>%
  mutate(skew2 = skewness(V1:V1998))

This creates a new column called skew2 however the skewness isn't calculated and instead the column is filled with "NaN". Does anyone know why this might be?

I'm using skewness from the moments package.

My data looks a little like this

Data                         V1       V2        V3    .....   V1998  ....
Acaricomes phytoseiuli        0.01    0.0       0.002         0.03
Acetivibrio cellulolyticus    0.005   0.002     0.011         0.04
Acetobacter aceti             0.001   0.003     0.004         0.0

Answer 1

You can do:

library(e1071)

# get column names
cols <- paste0('V', seq(1,1998,1))

# apply function on selected columns
NoDup2$skew_value <- apply(NoDup2[,cols], 1, skewness)

With this we calculate skewness for every row across all columns in the given data set.

Answer 2

I would try, but depends on what you want to do afterwards.

library(tidyverse)
iris %>% 
  gather(key, value, -Species) %>% 
  group_by(Species) %>% 
  mutate(skew2=moments::skewness(value)) %>% 
  slice(1:2)
# A tibble: 6 x 4
# Groups:   Species [3]
  Species    key          value skew2
  <fct>      <chr>        <dbl> <dbl>
1 setosa     Sepal.Length  5.10 0.146
2 setosa     Sepal.Length  4.90 0.146
3 versicolor Sepal.Length  7.00 0.157
4 versicolor Sepal.Length  6.40 0.157
5 virginica  Sepal.Length  6.30 0.128
6 virginica  Sepal.Length  5.80 0.128

I used the iris data as it is a more reproducible example. The idea is to gather the data. Then do the grouping and calculations. Afterwards you can spread the data back again. To get the skewness per row you can use:

iris %>% 
  gather(key, value, -Species) %>% 
  group_by(Species) %>% 
  summarise(skew2=moments::skewness(value)) 
# A tibble: 3 x 2
  Species    skew2
  <fct>      <dbl>
1 setosa     0.146
2 versicolor 0.157
3 virginica  0.128