如何避免R语言中DataFrame首列插入无表头数字列？

问题场景 #

处理如下格式的文件（file1.txt）：

number variant_id gene_id tss_distance ma_samples ma_count maf pval_nominal slope slope_se hg38_chr hg38_pos ref_allele alt_allele hg19_chr hg19_pos ID new_MAF CHROM POS REF ALT A1 OBS_CT BETA SE P SD Variance 
6253443 chr1_17726150_G_A_b38 ENSG00000272426.1 821374 68 78 0.0644628 0.764314 -0.0320846 0.106958 chr1 17726150 G A chr1 18052645 rs260514:18052645:G:A 0.058155 1 18052645 G A G 1597 0.0147047 0.0656528 0.822804 2.62364886486368 6.88353336610048
6253444 chr1_17726150_G_A_b38 ENSG00000117118.9 671980 68 78 0.0644628 0.955989 -0.00275742 0.0499406 chr1 17726150 G A chr1 18052645 rs260514:18052645:G:A 0.058155 1 18052645 G A G 1597 0.0147047 0.0656528 0.822804 2.62364886486368 6.88353336610048

执行以下代码删除首列number后：

Data <- read.table("/filepath_to_file/file1.txt", header = TRUE)
Data <- subset(Data, select = -number)
write.table(Data, "/filepath_to_file/file2.txt")

输出的file2.txt会多出无表头的行号列，且部分内容带引号，导致列名与值错位：

"variant_id" "gene_id" "tss_distance" "ma_samples" "ma_count" "maf" "pval_nominal" "slope" "slope_se" "hg38_chr" "hg38_pos" "ref_allele" "alt_allele" "hg19_chr" "hg19_pos" "ID" "new_MAF" "CHROM" "POS" "REF" "ALT" "A1" "OBS_CT" "BETA" "SE" "P" "SD" "Variance"
"1" "chr1_17726150_G_A_b38" "ENSG00000272426.1" 821374 68 78 0.0644628 0.764314 -0.0320846 0.106958 "chr1" 17726150 "G" "A" "chr1" 18052645 "rs260514:18052645:G:A" 0.058155 1 18052645 "G" "A" "G" 1597 0.0147047 0.0656528 0.822804 2.62364886486368 6.88353336610048
"2" "chr1_17726150_G_A_b38" "ENSG00000117118.9" 671980 68 78 0.0644628 0.955989 -0.00275742 0.0499406 "chr1" 17726150 "G" "A" "chr1" 18052645 "rs260514:18052645:G:A" 0.058155 1 18052645 "G" "A" "G" 1597 0.0147047 0.0656528 0.822804 2.62364886486368 6.88353336610048

期望输出格式为：

variant_id gene_id tss_distance ma_samples ma_count maf pval_nominal slope slope_se hg38_chr hg38_pos ref_allele alt_allele hg19_chr hg19_pos ID new_MAF CHROM POS REF ALT A1 OBS_CT BETA SE P SD Variance 
chr1_17726150_G_A_b38 ENSG00000272426.1 821374 68 78 0.0644628 0.764314 -0.0320846 0.106958 chr1 17726150 G A chr1 18052645 rs260514:18052645:G:A 0.058155 1 18052645 G A G 1597 0.0147047 0.0656528 0.822804 2.62364886486368 6.88353336610048
chr1_17726150_G_A_b38 ENSG00000117118.9 671980 68 78 0.0644628 0.955989 -0.00275742 chr1 17726150 G A chr1 18052645 rs260514:18052645:G:A 0.058155 1 18052645 G A G 1597 0.0147047 0.0656528 0.822804 2.62364886486368 6.88353336610048

原因分析 #

write.table()函数默认参数中：

• row.names=TRUE：会把数据框的行名（默认是1、2、3...）输出为新的首列
• quote=TRUE：会给字符型列的内容和列名添加双引号

这两个默认行为导致了输出格式不符合预期。

解决方案 #

方法1：修改write.table的参数 #

直接在write.table()中设置row.names=FALSE和quote=FALSE，同时指定sep=" "确保列之间用空格分隔（和原文件一致）：

Data <- read.table("/filepath_to_file/file1.txt", header = TRUE)
Data <- subset(Data, select = -number)
write.table(Data, "/filepath_to_file/file2.txt", row.names = FALSE, quote = FALSE, sep = " ")

方法2：用dplyr简化列删除操作（可选） #

如果习惯用dplyr包，可用select()函数删除列，代码更简洁：

library(dplyr)
Data <- read.table("/filepath_to_file/file1.txt", header = TRUE) %>%
  select(-number)
write.table(Data, "/filepath_to_file/file2.txt", row.names = FALSE, quote = FALSE, sep = " ")

方法3：用data.table快速读写（大文件推荐） #

如果处理大文件，data.table包的fread()和fwrite()效率更高，且默认不输出行名和引号：

library(data.table)
Data <- fread("/filepath_to_file/file1.txt")
Data <- Data[, !"number"]
fwrite(Data, "/filepath_to_file/file2.txt", sep = " ")

以上方法都能得到符合预期的输出格式，解决行号和引号问题。

内容的提问来源于stack exchange，提问作者HKJ3