从字符串中提取整数值

Question

我有一个形式的字符"RADIANCE_MULT_BAND_1 = 1.2412E-02"保存在变量中。我想提取整数值作为0.012412.请在 R 中建议语法。

Answer 1

# function to extract number from a string
f = function(x) {
y = unlist(strsplit(x, " "))
y = as.numeric(y)
y = y[!is.na(y)]
y }

# having one value
x = "RADIANCE_MULT_BAND_1 = 1.2412E-02"
f(x)
# [1] 0.012412

# having multiple values
dt = data.frame(x = c("RADIANCE_MULT_BAND_1 = 1.2412E-02",
"RADIANCE_MULT_BAND_2 = 1.5412E-02",
"RADIANCE_MULT_BAND_3 = 2.2412E-02"), stringsAsFactors = F)
dt$value = f(dt$x)
dt
#                                   x    value
# 1 RADIANCE_MULT_BAND_1 = 1.2412E-02 0.012412
# 2 RADIANCE_MULT_BAND_2 = 1.5412E-02 0.015412
# 3 RADIANCE_MULT_BAND_3 = 2.2412E-02 0.022412