如何使用 R 删除 dataframe 中的第一行和最后 N 行？

Question

I have a dataframe df of 2M+ rows that looks like this:

        LOCUS POS COUNT
1: CP007539.1   1     4
2: CP007539.1   2     7
3: CP007539.1   3    10
4: CP007539.1   4    15
5: CP007539.1   5    21
6: CP007539.1   6    28

Currently I am using this in order to remove the first and last 1000 rows:

> df_adj = df[head(df$POS,-1000),]
> df_adj = tail[(df_adj$POS,-1000),]

But even I can see that this can be done in a better way. Suggestions?

Answer 1

You can perform this specifying the range of rows you want to leave in the final dataset:

 df_adj <- df[1001:( nrow(df) - 1000 ),]

Just make sure you have enough rows to perform this. A safer approach might be:

df_adj <- if( nrow(df) > 2000 ) df[1001:( nrow(df) - 1000 ),] else df

Answer 2

Another way would be to combine seq_len with nrow and range :

df <- head(iris, 10)      
df[-range(seq_len(nrow(df))), ]

which will generate the output below:

# Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa
# 7          4.6         3.4          1.4         0.3  setosa
# 8          5.0         3.4          1.5         0.2  setosa
# 9          4.4         2.9          1.4         0.2  setosa