如何在Gnuplot中使用自定义函数将数值标签替换为字符串？

原脚本 #

set datafile separator "," 
set datafile commentschar '#'
set key autotitle columnhead # use the first line as title for data
set key noenhanced

function $labellookup(x) << EOF
    temp="null"
    if(x==2000){
    temp="two"
    }
    if(x==1000){
    temp="one"
    }
    if(x==3000){
    temp="three"}
    return temp
EOF

set yrange[*:*]

$DATA << EOD

t, v1, v2
0, 10, 3000
10, 11, 1000
15, 10, 4000
30, 11, 5000
38, 20, 6000
46, 11, 8000
47, 30, 1000
48, 31, 1000
49, 30, 4000
50, 31, 6000
51, 30, 9000
52, 30, 2000
61, 21, 3000
65, 20, 3000
70, 21, 4000
75, 10, 5000

EOD

# use column 1, and column 3 is the label; values
# are (x,y)=(column1, 2)
# column 2 is ignored

plot $DATA using 1:(2):3 with labels rotate by 90 left

修改方案 #

只需修改最后一行的plot命令，把直接引用第三列数值的部分，替换为调用$labellookup函数并传入第三列数值作为参数：

plot $DATA using 1:(2):(@$labellookup($3)) with labels rotate by 90 left

关键说明 #

• $3代表取当前行第三列的数值，作为参数传入$labellookup函数
• @$labellookup(...)是Gnuplot调用字符串函数的语法，用来展开函数返回的字符串作为标签内容
• 函数未匹配到的数值（比如4000、5000等），会返回预设的"null"作为标签

内容的提问来源于stack exchange，提问作者asylumax